Product Guides
WD-40 FAQ: What It's Actually For, What It's Not, and How to Use It Right
WD-40 is the water-displacing, penetrating, light-lubricating spray found in almost every Australian workshop and shed — this FAQ covers what it's actually for, what to avoid, whether it's a lubricant or a degreaser, safety and ingredients, how it compares to CRC 5-56, and how the Multi-Use and Specialist ranges differ.
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Epoxy Adhesive Guide
Epoxy adhesives and epoxy putty: 2-part mixing, cure times, what epoxy won't stick to, types by application, and product selection for Australian tradespeople and maintenance engineers.
Read moreChain Lube Guide: Wet, Dry, Wax & Industrial Types Explained
Every chain will wear — the question is how fast. Get the lubricant wrong, or skip it altogether, and you're not just shortening chain life; you're.
Read moreDrill Bit Types Guide
Grab a handful of drill bits from any toolbox and you will likely see several different colours, finishes and shapes. Ask most people what those.
Read moreGrease Selection Guide: Types, NLGI & EP
This guide is part of AIMS Industrial's curated Engineering Reference Charts library — 78 reference articles across fasteners, threading, bearings, lubrication and safety standards. Grease Types & Selection Guide: Lithium, EP, NLGI Grades & Compatibility Pick up two tubs of industrial grease from the same shelf and they may look identical — same colour, same consistency, same NLGI grade — and be completely incompatible. Mix them in a bearing housing and you can turn a reliable bearing into a failed one within a single shift. That's not an edge case; it's one of the most common causes of premature bearing failure in industrial maintenance. Grease selection is not complicated, but it requires understanding three things: what grease is actually made of, how to read the specification, and why mixing greases is a decision that needs to be made deliberately rather than by default. Get those three things right and greasing becomes systematic rather than guesswork. This guide covers every selection variable: thickener types, NLGI consistency grades, extreme pressure additives, temperature limits, food grade classifications, and the compatibility rules that determine what you can and cannot mix. There is also an application table to translate all of it into practical decisions for the most common industrial use cases. Contents What grease is made of Thickener types NLGI consistency grades EP additives and additive packages Operating temperature Application guide Grease compatibility — the mixing warning Food grade greases Dielectric grease How to re-grease correctly Frequently asked questions What grease is made of Grease is not oil with something added to make it thick. It is a structured product with three distinct components, and each plays a different role: Base oil — typically 75–95% of the total weight. The base oil is the actual lubricant — the film that separates surfaces and prevents metal-to-metal contact. Base oil viscosity is the primary determinant of load-carrying capacity and temperature performance. Most industrial greases use mineral base oil; high-performance greases may use PAO (polyalphaolefin) synthetic or ester synthetic base oils for extended temperature range and service life. Thickener — typically 3–30% of the total weight. The thickener is a solid or semi-solid matrix that holds the base oil in place and releases it gradually under shear at the lubrication point. The thickener is what makes grease a grease rather than an oil. Thickener type is the most critical selection variable — it determines temperature range, water resistance, and compatibility with other greases. Common thickeners include lithium soap, lithium complex, calcium soap, calcium sulphonate, polyurea, and bentone (clay). Additives — typically 1–10% of the total weight. Additives modify specific performance properties: extreme pressure (EP) additives improve load capacity under shock loading; anti-wear additives protect surfaces at low speed or boundary lubrication conditions; anti-oxidants extend service life; rust inhibitors protect ferrous surfaces from corrosion; tackifiers improve adhesion and resist fling-off; anti-foam agents prevent aeration in high-speed applications. The practical takeaway: two greases with the same NLGI grade and the same base oil viscosity can be incompatible if their thickeners are different. Specification matching must include the thickener type, not just the grade number. Thickener types The thickener is what most people mean when they say "type of grease." Understanding the main thickener families — their strengths, limits, and compatibility relationships — is the foundation of grease selection. Thickener type Max use temp (approx) Water resistance Load capacity Typical use Compatibility risk Lithium (simple) 120–130°C Good Medium (with EP: high) General purpose bearings, automotive, light industrial Low — compatible with most soap-based greases Lithium complex 150–180°C Good Medium–high High-temp bearings, industrial drives, conveyor systems Low — generally compatible with simple lithium Calcium (simple) 60–80°C Excellent Low–medium Wet environments, marine applications, chassis lubrication Low Calcium sulphonate complex 150–180°C Outstanding Very high (EP inherent) Severe industrial, steel mills, paper mills, mining, marine Low–moderate Polyurea 160–180°C Good Medium–high Electric motor bearings, sealed-for-life bearings HIGH — incompatible with soap-based greases Bentone / Clay 180–260°C Good Medium (with EP: high) Very high temperature applications, open gears, kiln bearings Moderate Sodium (soda) 120°C Poor — emulsifies in water Medium Legacy applications only — largely superseded Low Aluminium complex 150°C Very good Medium–high Food industry, wet environments Low–moderate Lithium grease — the default for good reason Simple lithium soap grease is the most widely used thickener type in the world, and for most general industrial applications, it is the correct default. It offers a good balance of temperature range, water resistance, mechanical stability, and cost. The drop point (the temperature at which the thickener structure collapses and the grease liquefies) is typically 175–200°C, giving a working maximum of around 120–130°C with reasonable service life. Lithium complex grease uses complexing agents during manufacture that raise the drop point above 260°C, extending the working temperature range to 150–180°C. Lithium complex is the appropriate upgrade when operating temperatures exceed the limits of simple lithium — not as a universal "better" choice, since it costs more and the compatibility matrix is slightly more complex. Calcium sulphonate — the specialist for severe conditions Calcium sulphonate complex grease has an unusual property: it provides inherent extreme pressure performance without sulphur-phosphorus EP additives. This makes it suitable for environments where conventional EP additives would degrade (very high temperatures, contact with water) or where sulphur-active metals must be protected. It also has outstanding water resistance, making it the preferred choice for steel mill work rolls, paper mill bearings, marine shafting, and mining equipment exposed to constant water contamination. Polyurea — excellent but incompatible Polyurea thickeners deliver excellent high-temperature performance, oxidation resistance, and compatibility with the seal materials common in electric motors and sealed bearings. For this reason, polyurea NLGI 2 grease is the factory fill in the majority of sealed electric motor bearings, and many bearing manufacturers specify it as the recommended re-grease product. The critical caveat: polyurea grease is incompatible with virtually all soap-based greases (lithium, lithium complex, calcium, sodium, aluminium complex). Mixing polyurea with lithium grease in a bearing housing can cause catastrophic softening or hardening within hours of startup, leading to rapid bearing failure. If an electric motor bearing is originally filled with polyurea grease, re-greasing must use polyurea grease — or the bearing must be thoroughly cleaned and repacked. Assuming "any NLGI 2 grease will do" in a motor bearing is a common and expensive mistake. NLGI consistency grades The National Lubricating Grease Institute (NLGI) consistency grade describes how stiff the grease is at 25°C. It is measured by the ASTM D217 cone penetration test — a weighted cone is dropped into the grease and the depth of penetration determines the grade. Lower numbers are softer (more fluid); higher numbers are stiffer. NLGI grade Consistency Appearance Typical applications 000 Semi-fluid Flows like heavy oil Centralised automatic lubrication systems, enclosed gear lubrication 00 Very fluid Very soft paste Centralised lubrication, low-temperature applications 0 Fluid Soft paste Low-temperature bearings, centralised lube systems, slow bearings at high load 1 Semi-fluid Soft butter Low-temperature or high-speed bearings, centralised lube systems 2 Smooth Peanut butter Default for most rolling element bearings, general industrial 3 Semi-firm Firm butter High-load or slow bearings, vertical shaft bearings, wheel bearings with high static loads 4 Firm Hard butter Open gears, sliding surfaces 5 Very firm Smooth wax Specialised open gear and slide applications 6 Hard Block / brick Open-air applications, very high ambient temperature, kiln trunnion bearings NLGI 2 — the default for most applications NLGI 2 is the correct starting point for most rolling element bearings operating at moderate speed and load. If the equipment documentation specifies no grade, and the operating conditions are unremarkable, NLGI 2 lithium or lithium complex grease is the default. The only common reasons to deviate from NLGI 2 are: NLGI 1 or 0: Required for low-temperature operation (below about −15°C) where NLGI 2 may be too stiff to distribute properly, or for high-speed bearings where a softer grease generates less churning heat. NLGI 3: Appropriate for high-load, low-speed applications (slow conveyors, vertical shaft bearings, heavily loaded wheel bearings) where a stiffer grease provides better retention and resistance to purging under load. NLGI 0 or 000: Required for centralised automatic lubrication systems where the grease must pump reliably through pipes and distribution fittings, often over long distances. EP additives and additive packages Extreme Pressure (EP) additives are chemical compounds — typically sulphur, phosphorus, or chlorine-based — that activate under high contact stress and high surface temperature to form a sacrificial boundary film on metal surfaces. This film prevents welding and scuffing under shock loads or slow, heavily loaded sliding contact where the hydrodynamic oil film would otherwise collapse. EP is an additive package, not a thickener type. This is the most common misconception in grease specification. "EP grease" means grease with extreme pressure additives; it does not say anything about whether the thickener is lithium, calcium, polyurea, or anything else. "Lithium EP 2" means: lithium thickener + EP additives + NLGI grade 2. Both axes must be specified. When EP is required Heavily loaded sliding contact: open gears, rack and pinion, ball and socket joints, chassis pivots Slow, high-load rolling element bearings: large industrial bearings operating below their speed rating with high radial or axial loads Shock and impact loading: crushers, presses, hammers Spline and coupling lubrication When EP is not required (and may be detrimental) High-speed, lightly loaded rolling element bearings — EP additives are not needed and some sulphur-based EP additives can attack yellow metals (copper, brass, bronze) in bearings or housings Applications with copper alloy components — confirm compatibility before using sulphur-active EP greases Food grade applications — most conventional EP additives are not approved for incidental food contact Operating temperature Temperature is one of the most important grease selection variables, and it is frequently underestimated. There are two temperatures that matter: Dropping point — the temperature at which the thickener structure irreversibly collapses and the grease becomes a liquid. This is a laboratory measurement. The dropping point is not the maximum use temperature; it is the failure point. Maximum continuous use temperature — typically 30–50°C below the dropping point, accounting for the fact that grease at the dropping point is already degraded before it liquefies. Sustained operation above the maximum continuous use temperature causes rapid oxidation of the base oil, hardening of the thickener, and loss of lubrication. A useful rule of thumb from bearing technology: grease service life approximately halves for every 10°C increase in bearing operating temperature above 70°C. A bearing running at 90°C will need re-greasing twice as often as the same bearing running at 70°C — and a bearing running at 110°C will need re-greasing four times as often. Grease type Drop point (approx) Max continuous use temp Min use temp (approx) Calcium (simple) ~100°C 60–70°C −30°C Sodium ~175°C 110–120°C −20°C Lithium (simple) 175–200°C 120–130°C −30°C Aluminium complex ~250°C 130–150°C −25°C Lithium complex >260°C 150–180°C −35°C Calcium sulphonate complex >300°C 150–180°C −25°C Polyurea 240–280°C 150–180°C −25°C Bentone / Clay None (no drop point) 180–220°C −20°C Note that bentone (clay) thickeners have no drop point — the thickener does not melt. This makes bentone greases technically useful at very high temperatures, but the base oil still oxidises at sustained elevated temperatures, so the practical maximum is still determined by base oil stability. Application guide The table below translates the selection variables into practical recommendations for the most common industrial applications. These are starting points — always verify against the equipment manufacturer's specification where it exists. Application Recommended thickener NLGI grade EP required? Notes General industrial rolling element bearings (moderate speed, load, temp) Lithium or lithium complex 2 Optional The default choice for most applications Electric motor bearings Polyurea 2–3 No Check OEM spec — many motors factory-filled with polyurea. Do not mix with lithium. High temperature bearings (>130°C) Lithium complex or calcium sulphonate 2–3 Optional Bentone for extreme temps >180°C Wet / water-contaminated environments Calcium sulphonate complex 2–3 Yes Outstanding water washout resistance; inherent EP Heavy industrial / mining / steel mill Calcium sulphonate complex 2–3 Yes (inherent) Superior to conventional EP greases under contamination and shock load Open gears, rack and pinion Lithium complex or bentone 3–4 Yes Tacky, adhesive products preferred to resist fling-off Centralised auto-lube systems Lithium or lithium complex 0–1 Optional Must pump at minimum ambient temperature; check pump specs Slow, heavily loaded plain bearings Lithium complex or calcium sulphonate 2–3 Yes Boundary lubrication conditions — EP essential Food processing equipment Aluminium complex or calcium sulphonate (NSF H1 rated) 2 NSF H1 approved only Must be NSF H1 certified for incidental food contact zones Electrical connections Silicone (dielectric grease) 2 No Not a bearing lubricant — for sealing and protecting electrical contacts only Roller chain drives Chain-specific oil or aerosol chain lube N/A No Do not use grease on roller chain — see roller chain lubrication guide Grease compatibility — the mixing warning When greases of different thickener types are mixed — either during a product changeover, when topping up without purging, or when an old and new grease meet in a bearing housing — the result can range from no effect to catastrophic failure depending on which two thickener types are involved. The mechanism varies. In some combinations the thickener structures interact chemically, causing the grease to soften dramatically and lose its ability to stay in place. In others the mixture hardens, blocking re-lubrication channels. In either case the base oil can separate from the thickener, depriving the bearing of lubrication. The compatibility matrix Thickener Lithium Li Complex Calcium Ca Sulph. Polyurea Bentone Lithium ✅ ✅ ✅ ⚠️ ❌ ⚠️ Li Complex ✅ ✅ ⚠️ ⚠️ ❌ ⚠️ Calcium ✅ ⚠️ ✅ ⚠️ ❌ ⚠️ Ca Sulphonate ⚠️ ⚠️ ⚠️ ✅ ⚠️ ⚠️ Polyurea ❌ ❌ ❌ ⚠️ ✅ ❌ Bentone ⚠️ ⚠️ ⚠️ ⚠️ ❌ ✅ ✅ Generally compatible | ⚠️ Borderline — test before use | ❌ Incompatible — do not mix Important caveat: Compatibility charts are a starting point, not a guarantee. A 2017 review of 17 published compatibility charts found significant contradictions between sources for several thickener combinations. The chart above reflects general consensus, but additive packages and base oil types within the same thickener family can change the outcome. When switching grease products on critical equipment, the safest approach is to clean and repack rather than top up. What to do when changing grease types If you need to switch from one thickener type to another — for example, moving from simple lithium to calcium sulphonate on a bearing exposed to water — the correct procedure is: Remove the bearing from service if possible. Clean out as much of the old grease as possible — disassemble and wipe, or flush with a compatible solvent. Repack with the new grease. If disassembly is not practical, purge by re-greasing repeatedly with the new product until the old grease is fully displaced and only the new grease exits the relief valve or purge point. Verify by colour or consistency if the two products are visibly different. For the polyurea/soap combination: do not attempt a purge procedure — the risk of the mixed zone causing bearing failure during the transition is real. Disassemble and repack. Food grade greases Food grade greases are required in food processing, beverage, pharmaceutical, and packaging operations wherever lubricant could come into contact with food or food-contact surfaces. They are classified by NSF International (formerly the National Sanitation Foundation) under three categories: NSF H1 — lubricants that may have incidental, technically unavoidable contact with food. This is the most commonly required classification for bearings, gearboxes, and conveyor components in food processing environments. H1 lubricants use food-safe thickeners (commonly aluminium complex or calcium sulphonate) and white mineral or PAO synthetic base oils. NSF H2 — lubricants used in areas with no possibility of food contact (machine room, external surfaces). H2 products are food-safe by formulation but not approved for incidental food contact. NSF H3 — edible oils or soluble oils used to clean and prevent rust on hooks, trolleys, and equipment that contacts food. Not a lubricating grease category. For all food processing bearing and machinery lubrication: specify NSF H1 rated products. H2 is not sufficient for in-plant equipment where product or packaging contact is possible. The NSF H1 rating must appear on the product label or technical data sheet — do not rely on a supplier's verbal assurance. A quality NSF H1 grease performs comparably to a conventional industrial grease of the same grade and thickener type under normal conditions. The performance compromise in food grade products is real at extreme temperatures or loads, but for most food processing environments operating at moderate speeds and temperatures, H1 greases are fully capable. Dielectric grease Dielectric grease is frequently searched in the same context as bearing and industrial greases, so it is worth being clear about what it is and what it is not. Dielectric grease is a silicone-based compound — typically silicone oil thickened with silica or a silicone wax — formulated to seal, insulate, and protect electrical connections. It is applied to spark plug boots, battery terminals, trailer connectors, switch contacts, and other electrical connection points to exclude moisture, prevent corrosion, and reduce the risk of arcing. It is not a lubricant in the bearing or machinery sense. The name "dielectric" refers to its electrical insulating properties — it does not conduct electricity and is used specifically because it will not short-circuit the connections it protects. Do not use dielectric grease as a bearing lubricant. Silicone grease has very poor mechanical stability under the shear and load conditions inside a bearing — the film it produces is inadequate for rolling contact loads, and its viscosity characteristics are not suited to either rolling or sliding lubrication under machinery conditions. The correct use of dielectric grease is electrical connection protection only. How to re-grease correctly Both under-greasing and over-greasing damage bearings — over-greasing is actually the more common cause of failure in maintained equipment, because it is less obvious. Understanding what happens inside a bearing housing explains why quantity and method both matter. What over-greasing does Bearings do not run in a housing full of grease. They run in a partially filled housing where only enough grease contacts the rolling elements to maintain the oil film. When a housing is over-filled with grease, the rolling elements churn through excess grease rather than running freely. This generates heat — sometimes enough to accelerate bearing wear faster than running dry would — and the churning pressure can force grease past seals, creating contamination pathways and seal damage. The rule of thumb for grease fill volume in a bearing housing is 30–50% of the free space at installation. The remaining space allows the grease to distribute, consolidate, and bleed oil without churning. For sealed-for-life bearings, this is handled by the manufacturer at assembly — do not attempt to add grease to a sealed bearing. Re-greasing quantity For re-greasing an open bearing in service, a rough starting formula for grease quantity is: G (grams) = 0.005 × D × B Where D = bearing outside diameter in mm, B = bearing width in mm. This is an approximation — use the equipment manufacturer's specification where available. Most bearing manufacturers publish re-greasing quantities and intervals in their catalogues for each bearing size and operating condition. Re-greasing frequency Re-greasing frequency is determined by bearing size, speed, temperature, contamination level, and grease type. As a general guide, the hotter and faster a bearing runs, the more frequently it needs re-greasing. Grease service life halves for every 10°C above 70°C — a bearing running at 90°C needs re-greasing twice as often as the same bearing at 70°C. For sealed and shielded bearings: these are not designed to be re-greased. They contain a calculated fill quantity at manufacture. Re-greasing attempts typically over-fill the housing and damage the seals. When sealed bearing grease life is exhausted, replace the bearing. Grease nipples and application Apply grease slowly through the grease nipple with the bearing running where safe to do so — this distributes the new grease evenly and allows displaced old grease to exit the relief valve. Applying grease rapidly to a cold, stationary bearing can build pressure that forces seals outward. If a relief valve is present, leave it open during re-greasing and close after the new grease appears at the outlet. See our comprehensive Grease Gun Guide for selection across manual lever, pneumatic and battery models, or the deep-dive Macnaught K29 Flexigun article for K29-specific technique. Choosing the right grease is the first step; applying and replenishing it correctly is the second. The bearing maintenance guide covers inspection intervals, relubrication procedures and storage best practices for all common industrial bearing types. CRC White Lithium Grease Heavy Duty (300 g) — General-purpose NLGI 2 lithium grease for bearings, hinges, slides, open gears, and general industrial applications. Good water resistance and temperature range for standard conditions. CRC Red Lithium Grease Aerosol (300 g) — Lithium EP grease in aerosol format for hard-to-reach lubrication points. Tackified formula resists fling-off on open mechanisms, chains, and exposed slides. Inplex 2163-220 Calcium Sulphonate Grease NLGI 3 — Severe-duty calcium sulphonate complex grease rated to 150°C with inherent EP performance and outstanding water resistance. Suited to pulp mills, steel mills, mining, and heavily loaded industrial bearings in contaminated environments. Browse the full range: Industrial Lubricants & Greases Frequently asked questions What is grease made of? Grease has three components: base oil (typically 75–95% by weight) which provides the actual lubricating film; a thickener (3–30%) which is a solid or semi-solid matrix that holds the base oil in place and releases it under shear; and additives (1–10%) which modify specific properties such as extreme pressure resistance, anti-corrosion performance, and oxidation stability. The base oil type and viscosity determine lubrication performance; the thickener type determines temperature range, water resistance, and compatibility with other greases. What does NLGI stand for and what do the grades mean? NLGI stands for National Lubricating Grease Institute. The NLGI consistency grade (0 through 6, plus semi-fluid grades 00 and 000) measures how stiff the grease is using a standardised cone penetration test at 25°C. Lower numbers are softer — NLGI 0 is a soft paste used in centralised lube systems; NLGI 2 is a smooth, firm consistency used in most general industrial bearings; NLGI 6 is a hard block grease used in high-temperature, open-air applications. NLGI 2 is the correct default for most rolling element bearing applications. What is the difference between lithium grease and lithium complex grease? Both use a lithium soap thickener, but lithium complex uses complexing agents during manufacture that significantly raise the dropping point — from around 175–200°C for simple lithium to above 260°C for lithium complex. This extends the working temperature range from about 120–130°C (simple lithium) to 150–180°C (lithium complex). The two are generally compatible and can be mixed, but lithium complex is more expensive. It is the correct upgrade when operating temperatures exceed simple lithium's limits — not a universal "better" choice for all applications. What is EP grease and when is it required? EP (Extreme Pressure) refers to an additive package — typically sulphur and phosphorus compounds — that forms a sacrificial protective film on metal surfaces under high contact stress and high surface temperature, preventing welding and scuffing. EP is an additive type, not a thickener type: "lithium EP 2" means lithium thickener + EP additives + NLGI grade 2. EP is required for heavily loaded sliding contacts (open gears, chassis pivots, splines), shock-loaded bearings, and slow heavy bearings operating in boundary lubrication conditions. It is generally not needed or beneficial for high-speed, lightly loaded rolling element bearings, and some sulphur-active EP additives can attack copper alloy components. Can you mix different types of grease? It depends on the thickener types involved. Lithium and lithium complex greases are generally compatible with each other and with simple calcium greases. Polyurea grease is incompatible with virtually all soap-based greases (lithium, calcium, sodium) — mixing polyurea with lithium grease in a bearing housing can cause catastrophic softening within hours of startup. Bentone (clay) greases are borderline compatible with most soap-based greases. When switching grease products on critical equipment, the safest approach is to clean out the old grease and repack rather than top up — especially if moving to or from a polyurea product. What grease should I use for electric motor bearings? Most electric motors are factory-filled with polyurea grease (typically NLGI 2 or 3), chosen for its excellent high-temperature performance, oxidation resistance, and compatibility with motor seal materials. If re-greasing is required, use the same type — polyurea NLGI 2 or whatever the motor manufacturer specifies. Substituting a lithium grease into a polyurea-filled motor bearing risks incompatibility. If the motor specification is not available, err toward a high-quality lithium complex NLGI 2 grease and purge thoroughly — but check the OEM documentation first. What temperature can lithium grease handle? Simple lithium soap grease has a dropping point of approximately 175–200°C and a practical maximum continuous use temperature of around 120–130°C. Lithium complex grease has a dropping point above 260°C and a practical maximum of 150–180°C. Both figures assume normal re-greasing intervals — grease service life halves for every 10°C above 70°C, so while simple lithium can technically operate at 130°C, the re-greasing interval at that temperature will be very short. If sustained high operating temperatures are expected, lithium complex or calcium sulphonate complex grease is the more practical choice. When should I use oil instead of grease for a bearing? Grease is the correct choice for approximately 80–90% of rolling element bearing applications. Oil lubrication is required when: (1) bearing speed is very high — above the speed factor threshold where grease churning heat becomes significant (typically above ndm = 300,000–500,000, where n is RPM and dm is the mean bearing diameter in mm); (2) operating temperatures are extreme and oil circulation is needed to dissipate heat; (3) the lubrication system needs to supply multiple points through a circulation circuit. For sealed, inaccessible, or infrequently maintained bearings, grease is strongly preferred because it stays in place and provides its own sealing function. What is food grade grease and when is it required? Food grade grease is formulated from ingredients approved for incidental food contact and classified by NSF International. NSF H1 grease may have technically unavoidable incidental contact with food and is required for bearings, conveyors, and equipment in food processing and packaging environments where contact with product is possible. NSF H2 grease is formulated from food-safe ingredients but not approved for incidental food contact — it is for machine room and inaccessible lubrication points only. The NSF H1 classification must appear on the product label or TDS. A quality H1 grease performs comparably to conventional industrial grease under normal food processing conditions. What is dielectric grease? Dielectric grease is a silicone-based compound used to seal and protect electrical connections — spark plug boots, battery terminals, trailer connectors, and similar. It is not a bearing or industrial lubricant. "Dielectric" describes its electrical insulating property. It does not conduct electricity and is used precisely because it will not short the connections it protects. Do not use dielectric grease as a bearing lubricant — silicone grease has inadequate mechanical stability and film strength for rolling contact applications. What does the colour of grease indicate? Nothing technically meaningful. Grease colour is determined by base oil colour, thickener colour, and any dyes added by the manufacturer. Red, blue, green, yellow, black, and white greases can all be the same NLGI grade and thickener type from different suppliers. Colour is a marketing and product differentiation tool, not a specification. The product data sheet — specifically the thickener type, NLGI grade, base oil viscosity, and dropping point — is the only reliable specification source. Never select a grease based on colour alone, and never assume that a "matching" colour means compatible products. How often should I re-grease a bearing? Re-greasing frequency depends on bearing size, operating speed, temperature, and contamination level. A rough guide: for a medium-sized industrial bearing (e.g. 60 mm bore) running at moderate speed (1,000 RPM) and moderate temperature (70°C), re-greasing every 2,000–3,000 operating hours is typical. Halve this interval for every 10°C above 70°C, or for heavily contaminated, wet, or vibration-intensive environments. The equipment manufacturer's maintenance schedule takes precedence over any general rule. For sealed bearings, re-greasing is generally not required or appropriate — replace the bearing when service life is exhausted. What is calcium sulphonate grease used for? Calcium sulphonate complex grease is used in severe industrial environments where conventional greases would fail: high water contamination (steel mills, paper mills, marine, food processing wash-down areas), high shock loads (mining, quarrying, presses), and high operating temperatures. Its key advantage is inherent extreme pressure performance derived from the calcium sulphonate complex chemistry itself — no sulphur-phosphorus EP additives are needed. This makes it suitable for environments where conventional EP additives would degrade or where the application requires NSF H1-rated products (some H1 calcium sulphonate greases are available). It costs more than lithium grease, but in severe environments the extended service intervals justify the premium. Need grease couplers? Browse the AIMS range at grease couplers. People Also Ask — Types of Grease Q: What is NLGI grade and what do the numbers mean? NLGI (National Lubricating Grease Institute) consistency grade classifies how firm or soft a grease is, using a scale from 000 (very fluid, almost liquid) to 6 (extremely firm, block-like). NLGI 2 is the most common industrial grade — firm enough to stay in place in typical bearing housings while soft enough to pump through fittings. NLGI 1 is used in centralised multi-point systems and cold-weather applications. NLGI 3 is used where grease must resist wash-out or where higher operating temperatures cause lighter grades to become too fluid. Q: What is the difference between lithium and lithium complex grease? Lithium grease uses a lithium soap thickener — it is the standard general-purpose grease for automotive and light industrial use, effective across a moderate temperature range. Lithium complex grease adds a complexing agent (typically lithium azelate or similar) to the soap structure, substantially extending the upper service temperature limit, improving water resistance, and increasing load-carrying capacity. Lithium complex is preferred for high-temperature applications, centralised greasing systems, and bearings with higher load. The two are generally compatible but confirm before mixing. Q: What does the thickener type mean for grease selection? The thickener holds the base oil in a semi-solid structure and determines many of the grease's performance characteristics. Common thickeners: lithium — general purpose, wide availability; lithium complex — extended temperature range; calcium — excellent water resistance, good for wet environments; polyurea — very high temperature, sealed-for-life bearings (electric motors); aluminium complex — water-resistant, tacky, good adhesion for open gears. The thickener type must match the application requirements, and incompatible thickeners should never be mixed. Q: When should I use a speciality grease versus a general-purpose grease? General-purpose lithium NLGI 2 covers the majority of workshop, maintenance and light industrial bearing applications. Speciality greases are required when: operating temperatures exceed the general-purpose range (use lithium complex or polyurea); loads are extremely high (use EP or high-load greases); the environment involves sustained water exposure (use calcium or calcium complex); food contact is possible (use NSF H1 food-grade grease); or the bearing operates at very high speed (use lighter NLGI 1 grade or low-viscosity speciality). Never substitute general-purpose grease in applications that specify a speciality product. Q: How long does grease last in a sealed bearing? Grease life in a sealed bearing depends on operating temperature, speed, load and the grease formulation. As a rough guideline, grease life approximately halves for every 15°C rise above 70°C. A sealed-for-life bearing in a lightly loaded, moderate-temperature application may last the life of the bearing without re-greasing. In heavy-duty, high-temperature or high-speed applications, even sealed bearings have a finite grease life and may require replacement at intervals rather than maintenance. Always follow the bearing and equipment manufacturer's recommendations.
Read moreRoller Chain: Sizes, Types & Sprockets
Industrial roller chain is not bicycle chain. That distinction matters, because if you search for "roller chain" or "sprockets" online, bicycle.
Read moreTorque Wrench Calibration: Standards, Intervals & Certificate Guide
A torque wrench in regular use will drift — gradually and invisibly — until it's applying meaningfully different torque than it reads. The click still fires. The number still appears on the display. Nothing signals that the tool has lost accuracy. A torque wrench that reads 100 Nm but applies 91 Nm is worse than useless: it gives false confidence while under-torquing every joint. Calibration catches and corrects this drift before it becomes a problem. This guide explains what torque wrench calibration involves, how often it's required, what ISO 6789 actually requires, and how to evaluate a calibration certificate. For guidance on choosing the right torque wrench in the first place, see our torque wrench selection guide. Need actual torque values once your wrench is calibrated? See our Metric Bolt Torque Chart or the Imperial/SAE Bolt Torque Chart for SAE Grade 2, 5 and 8 fasteners. Why Calibration Matters The case for calibration isn't just compliance paperwork. It's the difference between a fastener that holds and one that doesn't. In automotive work, an under-torqued wheel nut can work loose. In pipeline systems, under-torqued flange bolts allow gasket leakage. In structural steelwork, under-torqued high-strength bolts fail to achieve the required clamping force for friction-grip joints. Over-torquing is equally destructive: stretching bolts beyond yield, cracking cast components, crushing gaskets past their elastic recovery point. Beyond safety, calibrated torque tools are a requirement of ISO 9001 quality management systems. Clause 7.1.5 (Monitoring and measuring resources) requires that measuring equipment be calibrated or verified at specified intervals against measurement standards traceable to national or international measurement standards, with calibration records retained. A workshop that torques fasteners as part of its manufacturing or maintenance process needs documented calibration evidence to satisfy this requirement. The bottom line: calibration isn't optional maintenance — it's what gives a torque specification meaning. How Torque Wrenches Lose Accuracy Understanding the failure modes helps explain the calibration intervals. Spring fatigue (click wrenches): The coil spring in a click torque wrench is compressed and released with every tightening operation. Over thousands of cycles, the spring takes a permanent set — it compresses slightly shorter under the same force. This makes the mechanism click earlier than intended, delivering less torque than the set value. Impact damage: A single drop onto a hard floor — even from bench height — can shift internal components enough to change calibration measurably. Research indicates approximately 62% of accuracy issues with click-type torque wrenches are attributable to drops of more than 900 mm (roughly 3 feet) or repeated overloading. The problem is invisible: the wrench looks unchanged and continues to click on cue, but is no longer applying the correct torque. Overloading: Applying torque beyond the wrench's maximum rated capacity — particularly in reverse (using the wrench to loosen fasteners) — bends internal components and causes immediate, significant calibration loss. This is why torque wrenches should never be used as breaker bars. Transducer drift (digital wrenches): Electronic strain gauges can drift over time due to temperature cycling, mechanical stress, and electronic component ageing. Digital wrenches require calibration like any other type. Corrosion and contamination: Rust, grit, and dried lubricant in the mechanism can impede movement and cause inconsistent operation. Storage in poor conditions accelerates this. ISO 6789 — What the Standard Actually Requires ISO 6789 is the international standard governing the design and calibration of hand torque tools. The current version is ISO 6789-1:2017 (design conformance testing) and ISO 6789-2:2017 (calibration and measurement uncertainty). It replaced the earlier 2003 edition. ISO 6789 classifies torque wrenches into two types: Type Description Examples Type I — Setting type Signals when the set torque is reached — operator stops at the signal Click (micrometer), split-beam click, adjustable click Type II — Indicating type Displays or indicates torque throughout the application — operator reads the value Beam, dial, digital/electronic The accuracy requirement for both types is ±4% of the set or indicated value for the clockwise direction, across the rated operating range. Some manufacturers — including Stahlwille — build to ±2% for their precision ranges. ISO 6789-2:2017 requires calibration to be performed using traceable measurement standards — equipment whose accuracy is linked to national and international measurement references through an unbroken chain of comparisons. The calibration must cover the full operating range of the wrench, and the calibration certificate must state the measurement uncertainty. Calibration interval: ISO 6789 does not specify a fixed mandatory interval, but states that calibration should be performed at regular intervals and recommends no longer than 12 months or 5,000 operations — whichever comes first. For safety-critical applications (aerospace, energy, structural fastening), shorter intervals of 6 months or 2,500 operations are common practice. Your quality management plan should define the interval based on frequency of use and criticality of the application. Calibration vs Verification — What's the Difference? These two terms are often used interchangeably, but they mean different things in a quality management context. Calibration is the formal process of measuring a tool against traceable reference standards, determining any deviation from its specified performance, and adjusting the tool to bring it back within specification. Calibration produces a certificate documenting the results, the standard used, the measurement uncertainty, and the date and due date for the next calibration. Verification is a functional check — confirming that the tool reads within acceptable limits against a reference, but without necessarily correcting any deviation or producing a full calibration certificate. Verification is useful for in-process checking between formal calibration intervals. The Stahlwille SMARTCHECK torque wrench tester is an example of a verification tool: it allows you to check wrench accuracy in the field, catch a problem early, and remove a suspect wrench from service before the next scheduled calibration. For ISO 9001 compliance, calibration (with a traceable certificate) is required. Verification is a useful supplementary check but does not substitute for formal calibration records. What a Calibration Involves A professional torque wrench calibration typically includes: Testing across the full measurement range: The wrench is tested at multiple points throughout its rated range — not just at one value — to confirm accuracy is maintained across the operating spectrum. A wrench that reads correctly at 100 Nm but drifts at 50 Nm is not in calibration. Adjustment where required: If the wrench reads outside its accuracy specification at any test point, it is adjusted until it meets the required tolerance. For click wrenches, this typically involves adjusting the spring tension or the click mechanism. Calibration certificate: A calibration certificate is issued documenting the test results — the torque values applied, the readings obtained, the deviation from nominal, the measurement uncertainty, the standard used (e.g. DIN EN ISO 6789), the date of calibration, and the recommended date for the next calibration. Repair assessment: If the wrench shows signs of mechanical damage or wear that cannot be corrected by calibration adjustment, this is documented and the customer is contacted for a repair quote before any additional work proceeds. NATA Accreditation vs Manufacturer-Authorised Calibration In Australia, NATA (National Association of Testing Authorities) is the body that accredits calibration laboratories against ISO/IEC 17025 — the international standard for testing and calibration laboratory competence. A NATA-accredited calibration provides the highest level of formal traceability assurance available in Australia. However, NATA accreditation is not the only valid form of calibration for most applications. Calibration type Certificate standard Suitable for Required for NATA-accredited ISO/IEC 17025 + NATA endorsement All applications Defence, aerospace, medical, some government contracts Manufacturer-authorised (ISO 6789) DIN EN ISO 6789 Most ISO 9001, industrial, commercial Standard ISO 9001 QMS, most commercial manufacturing In-house verification Internal records only Supplementary spot-checks Not accepted as formal calibration evidence For most Australian industrial businesses — manufacturing, maintenance, construction, mining — a calibration certificate to DIN EN ISO 6789 from a competent, authorised calibration service is accepted by ISO 9001 auditors and provides the traceability required by the standard. If your quality plan or contracts specifically require NATA-accredited calibration, you will need to confirm this with your quality manager before selecting a calibration provider. What a Calibration Certificate Should Include Not all calibration certificates are equal. A valid calibration certificate to ISO 6789 should include the following: Certificate element Why it matters Tool identification (make, model, serial number) Links the certificate to a specific tool — not just a type Calibration standard referenced (e.g. DIN EN ISO 6789) Confirms the procedure used and the accuracy requirement applied Test results — applied torques and measured readings Shows actual performance across the range, not just a pass/fail Deviation from nominal at each test point Allows you to see how close to the limit the wrench is operating Measurement uncertainty Required by ISO 6789-2:2017 — quantifies the confidence interval of the measurement Date of calibration Establishes the start of the calibration interval Recommended next calibration date Supports your calibration scheduling and ISO 9001 records Calibration facility identification Identifies who performed the calibration and their authority A certificate that simply states "PASS — within specification" without test data is not a valid calibration certificate for ISO 9001 purposes. The actual measured values must be recorded. When to Calibrate — Not Just the Scheduled Date Scheduled intervals (12 months or 5,000 operations) are the baseline. Calibration is also required immediately in these circumstances: After any drop or impact: A wrench dropped onto a concrete floor — even with no visible damage — should be removed from service and sent for calibration before further use on any critical fastener. The damage is internal and invisible. After suspected overloading: If a wrench has been used beyond its rated capacity — either by exceeding maximum torque or by being used to loosen fasteners — calibrate before returning to service. When accuracy is suspect: If fasteners are consistently loose or over-torqued despite correct wrench technique, or if a beam wrench pointer doesn't return cleanly to zero with no load, investigate calibration before anything else. After extended storage: A wrench stored for 12 months or more — particularly in variable temperature conditions — should be verified or calibrated before returning to active use. Before critical work: For safety-critical assembly operations — structural bolted connections, pressure vessel flanges, engine rebuilds — calibrate immediately before use regardless of scheduled date, if the stakes of an incorrect torque are high enough. Record Keeping for ISO 9001 ISO 9001:2015 Clause 7.1.5.2 requires organisations to retain documented information as evidence of fitness for purpose of monitoring and measuring resources. In plain terms: keep your calibration certificates, maintain a calibration register (tool ID, calibration date, next due date, location), and be able to produce them on request during an audit. A calibration register doesn't need to be complex. A spreadsheet tracking each tool by serial number with calibration date, next due date, and certificate reference number is sufficient. The key is that the information exists, is current, and is accessible — and that any tool past its calibration due date is not in service on critical work. Stahlwille Torque Wrench Calibration — Available Through AIMS Industrial AIMS Industrial offers torque wrench calibration for Stahlwille tools through White International, the authorised Australian Stahlwille distributor. The service includes: Testing across the full measurement range of the tool Adjustment where required to bring the wrench back within specification A calibration certificate in accordance with DIN EN ISO 6789 Identification and quotation of any repairs required This calibration is manufacturer-authorised — performed by the distributor with direct knowledge of Stahlwille tools and access to the manufacturer's service procedures. The DIN EN ISO 6789 certificate is accepted for ISO 9001 quality management systems in most Australian industrial environments. To enquire about the calibration service, contact us here. Please include the tool model, serial number, and approximate last calibration date if known. We also stock the Stahlwille SMARTCHECK torque wrench tester for in-house verification checks between formal calibrations — available in 1–10 Nm and higher ranges. This allows your team to spot-check wrench accuracy in the field and identify any tool that may need early recalibration. Browse the AIMS Stahlwille torque wrench range → Frequently Asked Questions What is torque wrench calibration and why does it matter? Torque wrench calibration is the process of measuring a torque wrench against traceable reference standards, determining whether it performs within its accuracy specification, and adjusting it where necessary to restore correct performance. It matters because torque wrenches lose accuracy over time through spring fatigue, drops, overloading, and environmental exposure — and a wrench that has drifted out of calibration applies incorrect torque silently. The click still fires, the display still reads, but the actual torque applied is different from the set value. Calibration is what gives a torque specification its real-world meaning. How often should a torque wrench be calibrated? ISO 6789 recommends calibration at least every 12 months or every 5,000 operations — whichever comes first. For high-use tools or safety-critical applications (aerospace, pressure systems, structural steelwork), shorter intervals of 6 months or 2,500 operations are common. Calibration is also required immediately after any drop, overloading, suspected damage, or extended storage — regardless of where the tool sits in its scheduled interval. Your quality management plan should define intervals based on tool usage rate and application criticality. What is ISO 6789 and what does it require? ISO 6789 is the international standard for hand torque tools — covering both design conformance testing (ISO 6789-1:2017) and calibration requirements including measurement uncertainty (ISO 6789-2:2017). It classifies torque wrenches as Type I (setting type — click wrenches) or Type II (indicating type — beam, dial, digital). The accuracy requirement for both types is ±4% of the set or indicated value across the rated operating range. Calibration performed to ISO 6789 must use traceable measurement standards, test the full range of the tool, and document measurement uncertainty in the calibration certificate. What's the difference between calibration and verification? Calibration is a formal process: the tool is measured against traceable reference standards, adjusted if necessary, and a certificate documenting results and measurement uncertainty is issued. Verification is a functional check — confirming the tool reads within acceptable limits against a reference — but without formal adjustment or a full calibration certificate. Verification is useful for in-process spot-checking between calibration intervals. For ISO 9001 compliance, calibration records (with certificates) are required — verification alone does not satisfy the requirement. Does dropping a torque wrench affect its calibration? Yes — and often significantly. Research indicates that approximately 62% of accuracy issues with click-type torque wrenches are attributable to drops exceeding 900 mm or repeated overloading. Even a single drop onto a hard floor with no visible damage can shift internal components enough to take the wrench outside its accuracy specification. A dropped torque wrench should be removed from service on critical applications and sent for calibration before returning to use. Do not assume that an absence of visible damage means the wrench is still accurate. Should I store my torque wrench wound back to zero? Wind to the lowest scale setting — not to zero. Fully releasing the spring tension in some click wrench designs allows internal components (particularly the torque block) to shift out of alignment, which affects calibration. For a wrench in regular daily use, you don't need to adjust the setting between jobs. For storage of more than a few weeks, set it to the lowest marked scale value (not the zero stop) and store it in its case. Never store at a high torque setting long-term — this causes permanent spring set and calibration drift. Can I calibrate a torque wrench myself? Not to a standard that satisfies ISO 9001 or ISO 6789. Professional calibration requires a torque standard (a reference transducer or dead-weight machine) that is itself calibrated and traceable to national measurement standards. You can perform in-house verification using a torque tester — such as the Stahlwille SMARTCHECK — to check whether a wrench is reading within acceptable limits, which is useful for identifying a wrench that needs to be sent for formal calibration early. But this does not replace the calibration certificate required for quality management documentation. What should a torque wrench calibration certificate include? A valid calibration certificate to ISO 6789 should include: the tool's make, model and serial number; the calibration standard referenced (e.g. DIN EN ISO 6789); test results showing the applied torques and measured readings across the full range; the deviation from nominal at each test point; the measurement uncertainty; the date of calibration; the recommended next calibration date; and the identity of the calibration facility. A certificate that simply states "PASS" without recorded test data is not sufficient for ISO 9001 compliance. What is the difference between NATA and ISO 6789 calibration? NATA (National Association of Testing Authorities) accredits calibration laboratories in Australia against ISO/IEC 17025 — the international standard for laboratory competence. A NATA-accredited calibration provides the highest level of formal traceability assurance. ISO 6789 is the standard that defines how torque tools should be calibrated, including accuracy requirements and what the certificate must contain. A calibration can be performed to ISO 6789 without NATA accreditation — and this is accepted by most ISO 9001 auditors for standard industrial applications. NATA accreditation is specifically required for defence, aerospace, medical, and some government contracts. Is a manufacturer-issued calibration certificate acceptable for ISO 9001 audits? In most cases, yes — provided the certificate references a recognised standard (such as DIN EN ISO 6789), includes actual test data and measurement uncertainty, and is issued by a competent calibration facility. ISO 9001:2015 Clause 7.1.5.2 requires calibration against standards traceable to national or international measurement standards. It does not mandate NATA accreditation specifically. However, your quality management system, industry sector, or specific customer contracts may impose stricter requirements. If in doubt, confirm with your quality manager what level of traceability is required before selecting a calibration provider. How much does torque wrench calibration cost in Australia? Cost varies by provider, tool size, and whether repairs are required. For a standard click torque wrench, expect to pay in the range of $80–$200 for a professional calibration with a DIN EN ISO 6789 certificate. NATA-accredited calibration is typically at the higher end of the range or above, due to the additional overhead of laboratory accreditation. Calibration costs should be weighed against the cost of a mis-torqued joint — in most industrial applications, the calibration cost is a fraction of one warranty claim, rework event, or equipment failure. Do beam torque wrenches need calibration? Beam wrenches don't have a spring mechanism that fatigues, so they don't suffer calibration drift the way click wrenches do. However, they can be bent or damaged — particularly if used as a breaker bar or dropped — which shifts the zero point of the pointer. A beam wrench should be checked periodically: with no load applied, the pointer should sit at zero. If it doesn't, the wrench has been damaged and needs to be assessed. For ISO 9001 purposes, beam wrenches used for measured tightening should still be verified or calibrated on a documented schedule. How do I know if my torque wrench is out of calibration? The most common signs: the click fires earlier than expected (applying less torque than set); fasteners are consistently found loose after tightening to specification; the wrench was recently dropped or overloaded; the calibration certificate is expired; or a verification check on a torque tester shows readings outside the ±4% tolerance. In many cases there is no external sign — a drifted click wrench looks and operates identically to an accurate one. This is why scheduled calibration on a fixed interval is necessary, rather than relying on observable defects. What is the Stahlwille SMARTCHECK and can it replace professional calibration? The Stahlwille SMARTCHECK is a portable torque wrench tester that measures the output of a torque wrench against its own calibrated transducer, displaying whether the wrench is reading accurately. It's a verification tool — useful for in-house spot-checking between formal calibrations, and for catching a wrench that has drifted early before its scheduled calibration date. It does not replace professional calibration: it cannot adjust the wrench, it does not produce a calibration certificate to ISO 6789, and it does not satisfy the traceability requirements of ISO 9001. Use it as a first line of defence, not as a substitute for formal calibration records. For the matching spanner AF size on every common bolt, see our Spanner Size Chart. People Also Ask — Torque Wrench Calibration Q: How often should a torque wrench be calibrated? Most manufacturers and quality standards recommend calibrating a torque wrench at least once every 12 months under normal use, or after every 5,000 cycles, or after any event where the wrench may have been overloaded or dropped. Safety-critical applications such as aerospace and structural work often require shorter calibration intervals. Q: What happens if a torque wrench is not calibrated? An uncalibrated torque wrench may apply incorrect torque, either under-tightening fasteners which risks joint loosening, or over-tightening which can stretch or shear bolts and damage components. In safety-critical assemblies this can cause equipment failure or serious injury. Q: How is a torque wrench calibrated? A torque wrench is calibrated by applying known reference loads at a specified distance from the drive and measuring the wrench's output against a traceable reference standard. Professional calibration is performed using certified torque analyser equipment and produces a calibration certificate with traceability to national measurement standards. Q: Should I store a torque wrench at its lowest setting? Click-type torque wrenches should be wound back to their lowest setting after use to relieve tension on the internal spring mechanism and preserve calibration accuracy over time. Storing a click-type wrench at a set torque value compresses the spring continuously and can cause it to drift low over time. Does a torque wrench need calibrating in both directions? A click torque wrench is usually only rated and calibrated for clockwise (tightening) torque; using it to loosen can damage the mechanism and isn't covered by the calibration. Some digital and dual-direction wrenches are calibrated both ways — check the certificate for which directions were tested. Calibrate and use the wrench in the direction it's rated for. See torque wrenches. What does 'traceable to national standards' mean on a calibration certificate? It means the reference equipment used to calibrate your wrench was itself checked against a chain of higher standards leading back to a national measurement institute, so the reading is trustworthy and defensible in an audit. A NATA-endorsed certificate provides that traceability in Australia. For quality-system work, confirm the certificate states the traceability and the measurement uncertainty. See measuring tools. Is a digital torque wrench more accurate than a click type? A quality digital torque wrench typically holds a tighter accuracy tolerance and can log readings, but it still drifts and must be calibrated on the same schedule as a click wrench. Accuracy also depends on technique — a steady pull and correct hand position matter on both types. Buy to the accuracy the job needs, then keep it calibrated. See our torque wrench guide.
Read moreTorque Wrench Guide: Types, Sizes & How to Use It
Using a standard spanner to tighten a bolt feels definitive — but it gives you no feedback on how much force you've actually applied. Too loose and the joint fails. Too tight and you strip the thread, crush a gasket, or introduce stress that causes fatigue cracking later. A torque wrench removes the guesswork. It lets you apply a precise, controlled amount of rotational force — measured in Newton metres (Nm) or foot-pounds (ft-lb) — and stop exactly where the specification requires. This guide covers everything you need to select, set up and use a torque wrench correctly: the main types and when each makes sense, how to choose the right drive size and torque range, what Nm and ft-lb actually mean, and the common mistakes that quietly destroy accuracy. For information on maintaining that accuracy over time, see our torque wrench calibration guide. What Is a Torque Wrench? A torque wrench is a tool that applies a specified amount of torque — rotational force — to a fastener. Torque is calculated as force multiplied by the distance from the pivot point (T = F × d), which is why a longer handle lets you apply more torque with the same effort. The key distinction from a standard spanner is feedback. A spanner tells you nothing about how tight you've gone — you're relying on feel, which varies by operator, fatigue, and hand position. A torque wrench signals when you've reached the target: with a click, a visual indicator, or an audible alarm depending on the type. Torque specifications exist because fastener clamping force is critical to joint integrity. Under-torquing leaves the joint loose; over-torquing stretches or yields the fastener, compresses soft materials beyond recovery, or strips threads entirely. The specification is the engineered sweet spot — not a guideline. Types of Torque Wrench Five main types cover almost every industrial and workshop application. Each has a different signal mechanism, calibration characteristic, and ideal use case. Click (Micrometer) Torque Wrench The most widely used type in workshops and industry. You dial in the target torque by rotating the handle, which compresses an internal spring against a ball-and-detent mechanism. When the applied torque reaches the set value, the mechanism releases with an audible click and a small sideways movement of the head. Key characteristics: easy to set, works in confined spaces where you can't see a scale, requires no concentration on a dial. The limitation is the internal spring: it fatigues with use and compresses slightly over time, which causes calibration drift. Click wrenches need regular professional calibration — typically every 12 months or 5,000 operations, per ISO 6789. Storage note: wind the setting down to the lowest scale value before storing — not to zero. Fully releasing the spring tension in some designs can allow internal components to shift. Never store a click wrench at a high torque setting long-term. Split-Beam (Dual-Beam) Torque Wrench A variant of the click type that uses a separate, secondary beam to generate the click signal rather than a compressed spring. The drive head deflects against this beam at the set torque value, creating the click without repeatedly loading and unloading a coil spring. The practical advantage: calibration holds significantly longer because there's no spring to fatigue. Split-beam wrenches also don't need to be wound back after use — storage at any setting causes no spring set. They tend to cost more than standard click types, and the signal is slightly different in feel, but for high-use environments they offer better long-term accuracy retention. Beam (Deflecting Beam) Torque Wrench The simplest torque wrench design. A solid beam connects the handle to the drive head; a separate pointer beam stays straight while the main beam deflects under load. You read the torque from a fixed scale at the handle end as you apply force. There is no click — you must watch the scale while tightening, which requires direct line of sight and a steady hand. The advantage is mechanical simplicity: no spring, no mechanism, no calibration drift in the traditional sense. A beam wrench that reads correctly at the start will still read correctly years later, provided it hasn't been bent or damaged. Accuracy depends entirely on the operator reading the scale correctly under load. Beam wrenches are ideal where you want long-term reliability without recurring calibration cost, or in environments where a click mechanism might be mistaken for noise. They're less convenient in tight spaces and poor lighting. Digital (Electronic) Torque Wrench Uses a strain gauge transducer at the drive head to measure torque electronically and display it on an LCD screen. Most digital wrenches provide audible and visual alerts when the target torque is reached, and many add a secondary alert if the target is exceeded — allowing the operator to track over-torquing events. Digital wrenches offer the highest precision of any type in normal use, typically ±1–2%. They can usually store torque readings, switch between Nm, ft-lb, in-lb and kg-cm at the press of a button, and work in angle-torque mode (tracking degrees of rotation after a snug torque is reached — required for some engine and structural applications). The trade-offs are batteries, electronics that can be damaged by shock or moisture, and a higher purchase price. For production line work, quality-critical bolted joints, or applications that require electronic torque records, digital is the appropriate choice. Dial (Indicating) Torque Wrench Uses a dial gauge to display torque in real time as you apply it, similar in concept to a beam wrench but with a dial face instead of a deflection scale. Common in laboratory, quality control and low-volume precision assembly settings. Less common in general workshop use. Torque Screwdrivers For fasteners below the practical range of even a 1/4" drive torque wrench — typically under 5 Nm — a torque screwdriver is the correct tool. They're standard in electronics assembly, PCB work, ESD-sensitive environments, instrument panels, and any small precision fastener where a torque wrench's minimum setting is too coarse to give a reliable reading. Like torque wrenches, torque screwdrivers come in fixed and adjustable click formats, with interchangeable bits rather than a square drive. AIMS stocks the Wiha torque screwdriver range, including fixed and variable-torque models from roughly 0.5–5.0 Nm and ESD-safe versions for electronics work — see the torque screwdriver range for current options. Hydraulic and Pneumatic Torque Wrenches Used for very high torque values — typically above 1,000 Nm — where manual application isn't practical. Common in flanged pipe joints, structural steelwork, wind turbine assembly, mining, and heavy equipment maintenance. These are specialist tools outside the scope of most workshop applications. Comparison: Click vs Beam vs Digital Feature Click Split-Beam Beam Digital Signal when target reached Audible click + movement Audible click + movement None — read scale Beep + LED / vibration Typical accuracy ±4% (ISO 6789) ±4% (ISO 6789) ±3–4% ±1–2% Calibration drift Yes — spring fatigue Lower — no main spring Very low Low — transducer stable Works without line of sight Yes Yes No Yes Storage requirement Wind to lowest setting No requirement No requirement No requirement Unit switching Dual scale (Nm/ft-lb) Dual scale Dual scale Button — Nm/ft-lb/in-lb/kg-cm Angle mode No No No Yes (most models) Requires batteries No No No Yes Best for General workshop, automotive High-use, industrial Low-frequency, precision Critical joints, production Price range $50–$500+ $150–$800+ $40–$300+ $200–$2,000+ Drive Sizes — Choosing the Right Square Drive Torque wrenches connect to sockets via a square drive — the same system used by socket sets. The drive size determines the maximum torque the wrench can handle and the range of sockets available for it. Drive Size Typical Torque Range Best Applications 1/4" (6.35 mm) 2–25 Nm Precision assembly, bicycles, electronics, small fasteners, soft materials 3/8" (9.5 mm) 10–100 Nm General automotive, light machinery, most M6–M14 fasteners — the most versatile size 1/2" (12.7 mm) 28–300 Nm Heavy automotive (wheel nuts, cylinder heads), machinery bolts, structural M12–M20 3/4" (19.05 mm) 150–750 Nm Heavy industrial, large structural bolts, agricultural and mining equipment 1" (25.4 mm) 500–2,000+ Nm Flanged pipe joints, large industrial fasteners, heavy machinery, wind turbines If you're buying one torque wrench for general workshop use, 3/8" drive covers the majority of applications. If wheel nuts are on your list, add a 1/2" drive — most wheel nut torques (80–130 Nm) sit comfortably in 1/2" range. A 1/4" drive is worth adding if you work on bicycles, motorcycles or equipment with small precision fasteners. For wheel nut applications, the standard workflow is to use an impact wrench to run the nut down, then finish to specification with the torque wrench — see our impact driver vs impact wrench guide for choosing the right tool. You can adapt drive sizes using reducer or adapter sockets, but this introduces flex and reduces accuracy. Where possible, use the correct drive size for the job. Torque Range — How to Choose Every torque wrench has a minimum and maximum setting. The accuracy specification (typically ±4%) applies across the rated range, but real-world accuracy degrades at the extremes. As a rule: use a wrench where the target torque falls in the middle third of its range. For example, a wrench rated 20–100 Nm is most accurate between roughly 40–70 Nm. If you routinely torque at 25 Nm on this wrench, you're near the bottom of the range where accuracy suffers. A 10–50 Nm wrench would serve that job better. Common mistake: buying the widest-range wrench available to cover every job. A single 10–300 Nm wrench sounds versatile, but you'll consistently work at the extremes for many applications. Two wrenches with appropriate, overlapping ranges will always outperform one over-stretched wrench in accuracy. Nm vs ft-lb — Units and Conversion Australian engineering standards and most modern workshop manuals specify torque in Newton metres (Nm). Older manuals — particularly American and British sources — use foot-pounds (ft-lb) or inch-pounds (in-lb). Most torque wrenches have a dual scale showing both. To convert Multiply by Example Nm → ft-lb 0.7376 100 Nm = 73.8 ft-lb ft-lb → Nm 1.3558 80 ft-lb = 108.5 Nm in-lb → Nm 0.1130 50 in-lb = 5.65 Nm Nm → in-lb 8.8507 10 Nm = 88.5 in-lb Quick reference: 100 Nm ≈ 74 ft-lb. 1 ft-lb ≈ 1.36 Nm. Need actual torque values, not just the conversion? See our Metric Bolt Torque Chart or, for SAE fasteners, the Imperial/SAE Bolt Torque Chart for Grade 2, 5 and 8 values in ft-lb. Torque Wrench Accuracy — What ±4% Means in Practice ISO 6789 sets the accuracy standard for hand torque tools. For setting-type wrenches (click type), the requirement is ±4% of the set value in the clockwise direction. For indicating-type wrenches (beam, dial, digital), it's ±4% of the reading. At a practical level: a 100 Nm setting on a ±4% wrench means anywhere between 96 and 104 Nm of actual applied torque. For most workshop fasteners, this is perfectly acceptable. For critical applications — aerospace components, engine head bolts, structural flanges — tighter tolerances matter. Stahlwille's click torque wrenches are manufactured to ±2% accuracy, reducing the error band at 100 Nm to 98–102 Nm. This matters in environments where joint integrity is safety-critical, or where assembly records need to demonstrate tight process control. Accuracy also depends on how the wrench is used. Applying torque with a jerking motion consistently overshoots. Gripping the handle at the wrong point (too close to the head, or with a pipe extension) changes the effective lever arm and falsifies the reading. Pulling from the centre of the handle grip, smoothly and steadily, gives the most consistent results. How to Use a Torque Wrench Correctly Setting a torque wrench is only half the job. Consistent, accurate results depend on following the same correct technique every time you use a torque wrench — here's how, step by step. 1. Set the value before you start. For click wrenches, rotate the handle to the target Nm or ft-lb. Confirm the setting against the scale before applying any force. On digital wrenches, enter the target value and select the correct unit. 2. Check thread and surface condition. Torque specifications assume clean, dry threads unless otherwise stated. Lubricated threads (with oil, grease or anti-seize) require a reduced torque value — typically 75–80% of the dry specification — because lubricant reduces friction and increases actual clamping force at the same applied torque. Always check whether the spec is dry or lubricated. 3. Run the fastener down finger-tight first. Don't apply torque to a fastener that hasn't been snugged into its seat. Pre-load the joint by hand before using the wrench. 4. Apply force at the handle centre. Grip the handle in the middle of the marked grip zone. Applying force near the head reduces effective lever length and under-torques; applying at the very end increases it and over-torques. Keep your wrist straight and pull smoothly. 5. Stop at the signal. On a click wrench, one click means done — stop immediately. Continuing to apply force after the click adds torque beyond the target. On a digital wrench, stop when the alarm sounds. On a beam wrench, stop when the pointer reaches the mark. 6. Work in sequence on multi-bolt patterns. For flanges, cylinder heads, and any multi-bolt joint, tighten in a crossing pattern (star sequence) in stages — typically 30%, 60%, then 100% of final torque — to ensure even load distribution. Torquing each bolt to full value in one pass and moving to the next causes uneven clamping and potential distortion. 7. Don't check-click. Once a bolt is torqued, re-applying the wrench and clicking again tells you nothing useful — it will click at or near the set point whether the bolt is correct or slightly over. If you need to verify, back the fastener off slightly and re-torque from scratch. What NOT to Do with a Torque Wrench Mistake Why It Matters Using it as a breaker bar Loosening fasteners with a click wrench applies reverse torque far beyond the rated range, bending internal components and destroying calibration instantly Gripping the handle incorrectly Choking up toward the head or adding a pipe extension changes the effective lever arm and falsifies the reading — the wrench will click at the wrong torque Jerking or snapping the handle Impulse loading overshoots the target torque before the click mechanism can respond — particularly at lower torque settings Ignoring thread lubrication state Applying a dry torque spec to a lubricated fastener can result in 25–40% higher clamping force than intended — stretching or yielding the fastener Dropping it A single drop onto a hard floor can shift internal components enough to take the wrench outside its accuracy specification — even with no visible damage Storing at maximum setting Leaving a click wrench at high torque long-term causes spring set — the spring takes a permanent compression, reducing calibrated accuracy Winding to zero for storage In some click wrench designs, fully releasing spring tension allows the torque block to shift or fall out of alignment. Wind to the lowest scale setting, not zero Skipping calibration A click wrench that reads confidently but is out of calibration is worse than useless — it gives false confidence while applying incorrect torque Torque Wrench Selection Guide Application Typical Torque Range Recommended Drive Type Bicycle components (stem, seat post, handlebars) 4–25 Nm 1/4" Click or digital Motorcycle — general fasteners 10–60 Nm 3/8" Click Spark plugs 15–30 Nm 3/8" Click Oil drain plug 20–40 Nm 3/8" Click Wheel nuts (passenger vehicle) 80–130 Nm 1/2" Click Wheel nuts (light truck / 4WD) 100–200 Nm 1/2" Click Cylinder head bolts Varies — check manual 1/2" Digital (angle mode often required) General machinery — M8–M12 25–80 Nm 3/8" Click or split-beam General machinery — M14–M20 80–250 Nm 1/2" Click or split-beam Flanged pipe joints 100–500+ Nm 1/2" or 3/4" Click or digital Production line assembly Application-specific Match to fastener Digital (data recording) ISO 9001 documented tightening Application-specific Match to fastener Digital or calibrated click with certificate Stahlwille Torque Wrenches — When Accuracy Matters For applications where ±4% isn't tight enough — precision manufacturing, critical bolted joints, safety-regulated assemblies — Stahlwille torque wrenches offer a step up in accuracy and traceability. Manufactured to ±2% and backed by comprehensive calibration support through White International, Australia's authorised Stahlwille distributor, they're the appropriate choice when the cost of a joint failure outweighs the premium on the tool. AIMS Industrial stocks Stahlwille's click and electronic torque wrench range. We also offer torque wrench calibration services for Stahlwille tools through White International — with testing across the full measurement range and a calibration certificate to DIN EN ISO 6789. For more information, see our torque wrench calibration guide or contact us to discuss your requirements. Browse the AIMS torque wrench range → Frequently Asked Questions What is a torque wrench and why do I need one? A torque wrench applies a precise, controlled amount of rotational force (torque) to a fastener. You need one when a specification requires a fastener to be tightened to a particular value — typically stated in Newton metres (Nm) or foot-pounds (ft-lb). Without a torque wrench, you're guessing: too loose and the joint can loosen or leak; too tight and you risk stripping threads, crushing gaskets, or fatiguing the fastener to failure. Torque wrenches are standard in automotive, machinery, structural, and precision assembly work. What's the difference between a click, beam and digital torque wrench? Click wrenches use an internal spring mechanism that releases with an audible click when the set torque is reached. Beam wrenches use a deflecting arm and a fixed scale — no click, you read the torque visually as you apply force. Digital wrenches use an electronic strain gauge and give a beep or LED alert at the target torque, with the actual reading shown on an LCD. Click wrenches are the most common for general workshop use; beam wrenches need no calibration scheduling and are reliable long-term; digital wrenches are the most accurate and best suited for critical or recorded tightening applications. Which type of torque wrench is most accurate? Digital torque wrenches are typically the most accurate in normal use, rated at ±1–2%. Click and beam wrenches are rated at ±4% per ISO 6789 for most models. However, a well-calibrated click wrench from a quality manufacturer — such as Stahlwille, which achieves ±2% — will outperform a cheap digital wrench with a drifting transducer. Accuracy in practice depends on calibration status, correct technique, and appropriate range selection as much as it does on wrench type. What drive size torque wrench do I need — 1/4", 3/8" or 1/2"? 3/8" drive is the most versatile choice for general workshop use, covering approximately 10–100 Nm and most automotive and light machinery fasteners (M6–M14). If wheel nuts are a priority, add a 1/2" drive to cover the 80–200 Nm range. A 1/4" drive is worth having for precision work under 25 Nm — bicycles, motorcycles, electronics, and small fasteners in soft materials. If you're buying one wrench, start with 3/8". If you're equipping a workshop comprehensively, 3/8" and 1/2" together will cover 90% of applications. What torque wrench size do I need for wheel nuts? Wheel nut torque specifications vary by vehicle and stud size, so always check the manufacturer's figure rather than estimating. For passenger vehicles, a 3/8" or 1/2" drive torque wrench covering roughly 20–200 Nm is typically appropriate, matching the 80–130 Nm most wheel nuts require. For light trucks and 4WDs, stay within a 1/2" drive but expect the top of that range, 100–200 Nm. Heavy vehicles with larger studs need a 3/4" or 1" drive wrench capable of higher torque. See the Selection Guide table above for a fuller breakdown by application. What torque range should I buy? Choose a torque wrench where your most commonly used torque value falls in the middle third of the range. A wrench rated 20–100 Nm is most accurate between about 40–70 Nm. If you regularly work at 25 Nm, a 10–50 Nm wrench serves you better. Avoid buying the widest range available to cover everything — accuracy degrades at the extremes of any torque wrench's range. Two appropriately matched wrenches will outperform one overstretched wrench for accuracy. How do I set a torque wrench to the right value? On a click (micrometer) torque wrench, rotate the handle clockwise to increase and anti-clockwise to decrease the torque setting. The main scale on the handle body shows major increments; a secondary vernier or thimble scale on the rotating barrel shows fine increments. Add the two readings together to get the total set value. On a digital wrench, use the buttons to dial in the target torque and select the correct unit (Nm, ft-lb, in-lb). Always confirm the setting against the scale or display before applying torque. What do Nm and ft-lb mean, and how do I convert between them? Nm (Newton metres) and ft-lb (foot-pounds) are both units of torque — rotational force multiplied by distance from the pivot. To convert Nm to ft-lb, multiply by 0.7376. To convert ft-lb to Nm, multiply by 1.3558. Quick reference: 100 Nm ≈ 74 ft-lb. Most torque wrenches have a dual scale showing both units. Australian engineering standards and modern workshop manuals use Nm; older American and British manuals typically use ft-lb. Digital torque wrenches can switch between units at the press of a button. Can I use a torque wrench to loosen bolts? Technically yes, but it's not recommended for click wrenches. Applying reverse torque to a click wrench subjects the internal mechanism to loads it's not designed for and accelerates calibration drift. Beam wrenches are slightly more tolerant of reverse loads. If you need to loosen a fastener before using your torque wrench to re-torque it, use a standard ratchet or breaker bar for the loosening step, then swap to the torque wrench for the tightening step. Never use a torque wrench as a breaker bar for heavy loosening — this will damage the mechanism. Should I wind my torque wrench back to zero after use? Wind it to the lowest scale setting — not to zero. Fully releasing the spring tension in some click wrench designs allows internal components (particularly the torque block) to shift out of alignment. Winding to zero is also not necessary for short-term storage — a wrench in regular daily use doesn't need to be adjusted between jobs. For storage of more than a few weeks, set it to the lowest marked scale value (not the zero stop). Never store a click wrench at a high torque setting long-term, as this causes the spring to take a permanent set and lose calibrated accuracy. Can I use a torque wrench as a breaker bar? No. A torque wrench is a precision measuring instrument, not a force tool. Using it as a breaker bar — applying high reverse torque to loosen seized or over-torqued fasteners — will damage the internal mechanism of a click wrench, bend a beam wrench, and void calibration on any type. Use a dedicated breaker bar or a standard ratchet with a cheater bar for heavy loosening. Once the fastener is free, swap to the torque wrench for tightening. Why does my click torque wrench keep clicking at a lower torque than set? Premature clicking usually indicates the wrench is out of calibration — the internal spring has fatigued or the mechanism has drifted. It can also result from the setting being too low for the application, from reverse-loading the wrench repeatedly, or from a drop that shifted internal components. A torque wrench that clicks below its set value is applying less torque than you intend — this is a calibration issue that requires professional servicing, not field adjustment. Send the wrench for calibration before continuing to use it on critical fasteners. What is a split-beam torque wrench and is it better than a standard click type? A split-beam (or dual-beam) torque wrench uses a secondary beam to generate the click signal rather than a compressed coil spring. Because there's no main spring to fatigue, calibration holds more consistently over a higher number of operations. Split-beam wrenches don't need to be wound back after use, and they tend to maintain accuracy longer between formal calibration intervals. They cost more upfront but can be more economical for high-use environments. For infrequent workshop use, a quality standard click wrench with regular calibration is equally reliable. How long does a torque wrench last? A quality torque wrench — properly used, stored correctly, and calibrated on schedule — can last decades. Cheap wrenches may lose calibration quickly or fail mechanically within a few years of regular use. The limiting factor for click wrenches is usually spring fatigue, which is why ISO 6789 uses 5,000 operations as a calibration interval trigger. A beam wrench, having no spring, can outlast a click wrench significantly. Digital wrenches are limited by electronics and battery systems. Regular calibration identifies and corrects drift before it becomes a problem, effectively extending useful service life. When does a torque wrench need calibration? ISO 6789 recommends calibration at least every 12 months or every 5,000 operations, whichever comes first. Immediate calibration is also required after any drop, overloading, or unexpected impact — even without visible damage. For safety-critical applications (aerospace, energy, structural), shorter intervals (every 6 months or 2,500 operations) are common. For full details on calibration standards, intervals, and what a calibration certificate should include, see our torque wrench calibration guide. Need the right spanner for that bolt? Our Spanner Size Chart lists every common metric and imperial size. For metric to imperial socket cross-references and 1/4", 3/8" and 1/2" drive sizes, see our Socket Size Chart. Need tap wrenches? Browse the AIMS range at tap wrenches. Need open end wrenches? Browse the AIMS range at open end wrenches. Browse the full AIMS wrenches range.Correct torque and a threadlocker do different jobs and neither replaces the other — torque sets the clamping force, a threadlocker like Loctite 243 resists it working loose under vibration afterwards. See our Loctite Threadlocker Guide for grade selection by fastener size and service conditions.
Read moreCounterbore Drill Bits: Size Chart, Types & Countersink Comparison
Counterbore drill bits create a flat-bottomed cylindrical recess that allows a fastener head to sit flush with — or below — a surface. If you work with socket head cap screws, you need a counterbore. If you're reading an engineering drawing and see a stepped hole symbol you don't recognise, this guide explains exactly what it means and how to machine it. This guide covers the counterbore vs countersink decision, metric size charts for socket head cap screws (M3–M24), drawing symbols, tool types, and how to select the right bit for steel, aluminium, and cast iron. Counterbore Size Chart for Metric Socket Head Cap Screws — Quick Reference The chart below covers ISO 4762 socket head cap screws from M3 to M24, which covers the great majority of industrial assembly and maintenance work. Two fit classes are shown: close fit (tighter clearance, better alignment, for precision assemblies) and normal fit (standard worksh. Screw Size Close Fit — A (mm) Normal Fit — A (mm) Counterbore Ø — X (mm) Counterbore Depth — H (mm) M3 3.2 3.4 6.5 3.0 M4 4.3 4.5 8.5 4.0 M5 5.3 5.5 10.0 5.0 M6 6.4 6.6 11.0 6.0 M8 8.4 9.0 14.5 8.0 M10 10.5 11.0 18.0 10.0 M12 13.0 13.5 20.5 12.0 M16 17.0 17.5 26.5 16.0 M20 21.0 22.0 33.0 20.0 M24 25.0 26.0 40.0 24.0 What Is a Counterbore? A counterbore is a cylindrical flat-bottomed recess machined concentric to an existing hole. It has two diameters: the smaller clearance hole for the bolt shank, and the larger recess sized to accept the fastener head. The walls of a counterbore are vertical and the base is flat — there is no taper. The purpose is to allow a fastener to sit at or below the surface of the workpiece. This is required when a protruding bolt head would interfere with a mating component, create a safety hazard, or simply needs to be hidden for aesthetic reasons. The Three Hole Types: Counterbore, Countersink, and Spotface These three are frequently confused on the workshop floor and on engineering drawings. They are not interchangeable. Hole Type Shape Bottom Profile Used For Counterbore Cylindrical recess Flat Socket head cap screws, button head screws, hex head bolts below surface Countersink Conical recess Tapered (60°, 82°, 90°, or 120°) Flat head (CSK) screws, rivets, deburring Spotface Very shallow cylindrical recess Flat Creating a clean flat seating face on rough or cast surfaces — not for sinking the head A spotface is essentially a very shallow counterbore — typically just deep enough to clean the surface and provide a flat bearing face for a washer or bolt head. It does not sink the fastener head below the surface. Counterbore vs Countersink: Which Do You Need? The answer comes down to one thing: the geometry of your fastener head. Head Geometry Determines the Choice If your fastener has a flat conical underside (a flat head or CSK screw), you need a countersink. The conical recess matches the taper of the head and draws the screw flush as it's tightened. If your fastener has a flat bottom and cylindrical or hex head (socket head cap screw, button head screw, hex bolt you want to recess), you need a counterbore. The flat base of the recess provides a proper bearing face for the flat underside of the head. Fastener Type Head Shape Use Socket head cap screw (Allen bolt) Cylindrical, flat base Counterbore Button head socket screw Domed, flat base Counterbore Flat head (CSK) screw Conical underside Countersink Pan head / cheese head screw Flat top, flat base Counterbore (if recessing) or plain clearance hole Hex bolt (recessed) Hex head, flat base Counterbore Strength Considerations A counterbored joint is generally stronger than a countersunk one for the same bolt size. A socket head cap screw in a counterbore can be torqued to its full specification because the cylindrical head bears on a flat face. A countersunk screw relies on the taper of the head wedging into the recess — over-torque and you pull the head into the material, stripping the recess or splitting the screw head. Material Thickness Counterbores require adequate material thickness beneath the recess. As a rule of thumb, you need at least 1.5× the socket head height remaining below the counterbore base to maintain joint integrity. In thin sheet metal where this is not possible, a countersunk screw is the practical choice even if a counterbore would otherwise be preferred. Counterbore Size Chart for Metric Socket Head Cap Screws The chart below covers ISO 4762 socket head cap screws from M3 to M24, which covers the great majority of industrial assembly and maintenance work. Two fit classes are shown: close fit (tighter clearance, better alignment, for precision assemblies) and normal fit (standard workshop use). How to Read the Chart Three dimensions define a counterbored hole for a given screw size: Clearance hole diameter (A) — the through-hole for the bolt shank. Drill this first. Counterbore diameter (X) — the diameter of the flat-bottomed recess. This must match or slightly exceed the socket head diameter of the screw. Counterbore depth (H) — how deep to machine the recess. This equals the socket head height so the top of the head sits exactly flush. Machine slightly deeper if you want the head to sit below the surface. Metric Counterbore Dimensions — ISO 4762 Socket Head Cap Screws Screw Size Close Fit — A (mm) Normal Fit — A (mm) Counterbore Ø — X (mm) Counterbore Depth — H (mm) M3 3.2 3.4 6.5 3.0 M4 4.3 4.5 8.5 4.0 M5 5.3 5.5 10.0 5.0 M6 6.4 6.6 11.0 6.0 M8 8.4 9.0 14.5 8.0 M10 10.5 11.0 18.0 10.0 M12 13.0 13.5 20.5 12.0 M16 17.0 17.5 26.5 16.0 M20 21.0 22.0 33.0 20.0 M24 25.0 26.0 40.0 24.0 Dimensions per ISO 4762 and consistent with ASME B18.3 metric series. Clearance hole diameters per ISO 273 (close and normal fit classes). Always verify against your fastener supplier’s actual head dimensions — some aftermarket socket screws vary slightly from the ISO nominal. When the Chart Does Not Apply This chart is for ISO 4762 socket head cap screws only. Button head socket screws (ISO 7380), low-head socket screws, and non-standard grades have different head diameters and heights. Always check the screw datasheet if you are counterboring for anything other than a standard socket head cap screw. Counterbore Symbols in Engineering Drawings Engineering drawings use standardised symbols to call out counterbored holes. If you're machining from a drawing and see an unfamiliar symbol next to a hole dimension, it's likely one of these. The Standard Counterbore Symbol The counterbore symbol is a square with a horizontal line across the bottom — ⌴ (Unicode ⌴). In older drawings you may also see the abbreviation C’BORE or CBORE. The symbol is always followed by the counterbore diameter and depth. How to Read a Counterbore Callout A typical counterbore callout reads as a stack of two dimensions: Top line: clearance hole diameter and depth (or “THRU” for through-holes) Bottom line: counterbore symbol + counterbore diameter × counterbore depth Example callout for an M6 counterbored hole: ⌀6.6 THRU⌴ ⌀11 ↓ 6 This means: drill a 6.6 mm through-hole, then counterbore to 11 mm diameter to a depth of 6 mm. Counterbore vs Countersink Drawing Notation Feature Symbol Abbreviation Dimension given Counterbore ⌴ C’BORE / CBORE Diameter × depth Countersink ⌵ C’SINK / CSK Diameter × included angle Spotface ⌴ (shallow) SF / SFACE Diameter × depth (depth often minimal or not specified) Depth symbol ↓ — Used with all hole types to denote depth Types of Counterbore Drill Bits Not all counterbore tools work the same way. Choosing the wrong type for your setup is the most common cause of off-centre counterbores and chattered finishes. Piloted vs Non-Piloted Counterbore Bits A piloted counterbore bit has a small pilot pin at the centre that locates in the pre-drilled clearance hole. The pilot keeps the counterbore concentric with the clearance hole and prevents wandering. This is the correct choice for freehand drilling or when working on a drill press without a precision fixture. A non-piloted counterbore bit (also called a flat-bottom or end mill style counterbore) has no pilot. It requires the workpiece to be precisely fixtured or machined on a mill to guarantee concentricity. On a hand drill without fixturing, a non-piloted bit will wander. For maintenance and fabrication work — the majority of AIMS customers — a piloted bit is the practical choice. 180-Degree Counterbore Drill (Combined Drill and Counterbore) The Bordo 3871 range stocked by AIMS is a 180-degree counterbore drill: a combined tool that drills the clearance hole and counterbore in a single operation. The pilot tip drills the clearance hole, and the larger-diameter cutting section machines the counterbore simultaneously as the tool plunges. Note: this is different from a centre drill bit (also called a "combined drill and countersink" — DIN 333 or ANSI B94-11), which produces a 60° conical hole for lathe tailstock support and is sized by pilot diameter rather than counterbore diameter. Confirm which tool you actually need before ordering — the names overlap but the applications are entirely separate. This is the fastest option when you are drilling fresh holes and counterboring in one step. It is not suitable for counterboring an existing hole — for that, use the Bordo 3870 (counterbore only, no pilot drill) or the Sutton Tools C100 DIN373. Counterbore-Only Bits (No Pilot Drill) The Bordo 3870 and Sutton Tools C100 DIN373 are counterbore-only tools with a pilot. They locate in a pre-drilled hole and machine only the counterbore recess. Use these when: The clearance hole is already drilled and you need to add a counterbore You are reworking an existing component You need to control clearance hole diameter and counterbore diameter independently The Sutton Tools C100 is manufactured from cobalt steel (HSS-E) to DIN 373, making it the preferred choice for harder materials including stainless steel and alloy steels. HSS vs Cobalt Steel Counterbore Bits Grade Suitable Materials Notes HSS (High Speed Steel) Mild steel, aluminium, brass, plastics, timber Good all-rounder for general fabrication. Lower cost. HSS-E (Cobalt 5%) Stainless steel, high-tensile alloys, cast iron, hardened steels Better heat resistance. Runs at slower speeds but holds edge longer in tough materials. DIN 373 specification. For mild steel and aluminium in a standard workshop, HSS is adequate. For stainless steel fastener applications or hardened components, invest in cobalt (HSS-E). Forcing an HSS bit through stainless steel at the wrong speed will blunt it quickly and produce a poor finish. Reverse (Back) Counterbore Tools A back counterbore (also called a reverse counterbore) machines a counterbore on the underside of a plate or component — the side you can't access directly with a standard tool. These are specialist tools used in structural steel, pressure vessel, and pipe flange work where both faces need to seat fasteners. Back counterbore kits are available on request — contact the AIMS team for sourcing. How to Counterbore a Hole Step 1: Drill the Clearance Hole First Mark and drill the clearance hole to the correct diameter for your screw size and fit class (refer to the size chart above). Ensure the hole is perpendicular to the surface — a crooked clearance hole will produce a crooked counterbore regardless of how carefully you set up the counterbore tool. Step 2: Select the Correct Counterbore Tool Match the counterbore diameter to the screw head diameter from the size chart. If using a piloted tool, the pilot must match your clearance hole diameter. Most Bordo 3870 and 3871 sets are designated by screw size (e.g., “for M6 screw”), which takes the guesswork out of matching pilot to clearance hole. Step 3: Set the Depth Stop On a drill press, set the depth stop to the counterbore depth from the chart. If you want the fastener head to sit 1–2 mm below the surface (for example, to be filled with a plug), add that amount to the depth stop setting. For hand drilling without a depth stop, wrap tape around the counterbore shank at the correct depth as a visual marker. Step 4: Machine the Counterbore Run at the appropriate cutting speed for your material (see the table below). Feed firmly but without excessive pressure. A piloted tool should self-locate in the clearance hole — do not force it in sideways. The cut should be smooth; chatter or squealing indicates too high a speed or insufficient feed pressure. Cutting Speed Reference Material HSS (m/min) Cobalt HSS-E (m/min) Mild steel 15–25 20–30 Alloy steel / high tensile 8–15 12–20 Stainless steel 5–10 8–15 Cast iron 15–20 20–25 Aluminium 40–60 40–60 Use cutting fluid on steel and stainless. Aluminium can be run dry or with light oil. Always use cutting fluid on cast iron? No — machine cast iron dry; coolant causes thermal shock and can crack the iron. Troubleshooting: Off-Centre Counterbores If the counterbore is not concentric with the clearance hole, the cause is almost always one of three things: Pilot too loose: the pilot diameter is smaller than the clearance hole, allowing the tool to walk. Use a close-fit clearance hole or select a piloted tool sized correctly for your hole. Non-piloted tool used freehand: without a pilot and without fixturing, wandering is unavoidable. Switch to a piloted bit or use a mill. Clearance hole is itself off-centre: the counterbore is machined concentric to the pilot hole. If the pilot hole is in the wrong place, so is the counterbore. Remark and redrill. Counterbore Tool Selection Guide By Application Application Recommended Tool Stocked by AIMS Drilling fresh holes + counterboring in one pass (mild steel) 180° counterbore drill (combined) Bordo 3871 Counterboring existing holes (mild steel) Piloted counterbore, HSS Bordo 3870 Counterboring in stainless or alloy steel Piloted counterbore, cobalt HSS-E, DIN 373 Sutton Tools C100 High-volume production or workshop set (M3–M10) Counterbore set Bordo 3870-SET or 3871-SET By Material For mild and low-alloy steel, the Bordo HSS range handles the job comfortably at standard workshop speeds. Use cutting oil and maintain a consistent feed rate. For stainless steel, use the Sutton Tools C100 cobalt HSS-E. Run at reduced speed (half the speed you'd use for mild steel), apply cutting oil liberally, and avoid dwelling — keep the tool moving to prevent work-hardening at the cut face. For aluminium, HSS runs well at high speed with light oil or dry. Keep flutes clear of swarf build-up, which can weld to the cutting edge in aluminium at high temperatures. For cast iron, use HSS or cobalt at moderate speed, machine dry, and clear swarf regularly. Cast iron is brittle — use moderate feed pressure and avoid vibration. Browse AIMS Industrial’s full counterbore range: Counterbore Drill Bits & Sets Frequently Asked Questions What is a counterbore used for? A counterbore creates a flat-bottomed cylindrical recess that allows a fastener head — typically a socket head cap screw — to sit flush with or below the surface of a workpiece. It is used wherever a protruding bolt head would cause interference, create a hazard, or is not acceptable for design reasons. What is the difference between a counterbore and a countersink? A counterbore has vertical walls and a flat bottom; it is used for fasteners with flat-bottomed cylindrical heads (socket head cap screws, button heads). A countersink has angled walls forming a cone; it is used for fasteners with a tapered conical head (flat head or CSK screws). The choice is determined entirely by the geometry of the fastener head. What is the difference between a counterbore and a spotface? Both produce a flat-bottomed cylindrical recess, but a spotface is very shallow — just deep enough to create a clean flat bearing face on a rough or as-cast surface. A spotface does not sink the fastener head below the surface. A counterbore is deeper and is sized to accept the full height of the fastener head. How do I work out the correct counterbore diameter and depth? For metric socket head cap screws (ISO 4762), use the size chart in this article. The counterbore diameter must equal or very slightly exceed the socket head diameter (column X), and the counterbore depth must equal or slightly exceed the socket head height (column H). If you want the fastener to sit below the surface, add the desired recess depth to H. What is a piloted counterbore bit and do I need one? A piloted counterbore bit has a small-diameter pilot pin that locates in the pre-drilled clearance hole to keep the counterbore concentric. For drill press and hand drill work, a piloted bit is essential — without it, the larger cutting diameter has no reference to align to and will wander. Only omit the pilot if the workpiece is fixtured on a milling machine with the tool precisely aligned. What does the counterbore symbol look like on an engineering drawing? The counterbore symbol is ⌴ — a square with a horizontal line across the bottom. It appears before the counterbore diameter dimension. Older drawings may use the abbreviation C’BORE or CBORE instead. The depth is given after a down-arrow symbol (↓). Can I use a counterbore drill bit on wood? Yes, counterbore bits work on timber and engineered wood products. They are commonly used in furniture and joinery to recess bolt heads so they can be plugged for a clean finish. For wood, HSS at high speed works well. Bordo and Sutton counterbore bits are designed primarily for metal but will perform in wood. What is the difference between a 180-degree counterbore drill and a standard counterbore bit? A 180-degree counterbore drill (like the Bordo 3871) is a combined tool that drills the clearance hole and machines the counterbore recess in a single plunge. It is the fastest option when starting from solid material. A standard counterbore bit (like the Bordo 3870 or Sutton C100) only machines the counterbore recess — the clearance hole must be pre-drilled. Use a standard counterbore bit when reworking an existing hole. Should I use HSS or cobalt for counterboring stainless steel? Cobalt HSS-E (such as the Sutton Tools C100 DIN 373). Stainless steel work-hardens rapidly when cut at incorrect speeds or when the tool dwells without feeding. Cobalt steel holds its cutting edge at higher temperatures than standard HSS and is the correct choice for stainless, high-tensile alloy steels, and any application where HSS bits are burning out prematurely. What is a reverse counterbore (back counterbore) tool? A reverse or back counterbore tool machines a counterbore on the underside (blind face) of a plate or component — the face you cannot access directly from above. The tool is fed through the clearance hole, then a cutting head deploys perpendicular to the shank to machine the recess from the back. They are used in structural, pressure vessel, and pipe flange applications. Contact the AIMS team to source back counterbore tooling for your application. How do I stop a counterbore from going off-centre? Use a piloted counterbore bit sized correctly for your clearance hole. The most common cause of off-centre counterbores is a pilot pin that is smaller than the clearance hole, allowing the tool to shift. Ensure the clearance hole itself is accurately positioned before counterboring — the counterbore machines concentric to whatever hole the pilot locates in. Can I counterbore by hand (without a drill press)? Yes, with a piloted counterbore bit. The pilot locates in the clearance hole and guides the tool to stay concentric. Keep the drill as square to the surface as possible and use a depth marker (tape on the shank) to control depth. A drill press produces more accurate and repeatable results, but for site work and maintenance applications a hand drill with a piloted bit is practical. AIMS Industrial stocks counterbore drill bits and sets from Bordo and Sutton Tools, available for immediate dispatch across Australia. Browse counterbores and sets or call our team on (02) 9773-0122 for application advice. For metric bolt diameter, pitch and head dimensions from M3 to M24, see our Metric Bolt Size Guide. People Also Ask — Counterbore and Countersink Drill Bits Q: What is the difference between a counterbore and a countersink? A counterbore creates a flat-bottomed cylindrical recess that allows a socket head cap screw or button head screw to sit flush with or below the workpiece surface. A countersink creates a conical recess that matches the taper of a flat-head (countersunk) screw, allowing the screw head to seat flush with the surface. Q: How do I select the correct counterbore size for a socket head cap screw? The counterbore diameter must be slightly larger than the screw head diameter, and the counterbore depth must equal or slightly exceed the screw head height. Reference counterbore size charts matched to the screw thread size and head standard, as for metric socket cap screws the head diameter is typically 1.5 to 1.6 times the nominal thread diameter. Q: What included angle should a countersink have for metric flat-head screws? Metric flat-head (countersunk) screws typically use a 90-degree included angle for the head taper as specified in ISO standards. This differs from some imperial countersunk screws which use an 82-degree angle. Using the wrong countersink angle results in the screw head either rocking in the recess or not seating fully flush. Q: Can I use a standard twist drill to create a counterbore? A twist drill creates a conical-bottomed hole, not a flat-bottomed counterbore. To produce a proper flat-bottomed counterbore you need a dedicated counterbore tool with a flat end and a pilot pin to keep it concentric with the existing hole. Attempting to counterbore with a twist drill leaves an uneven floor that prevents the screw head from seating correctly. Need pan head screws? Browse the AIMS range at pan head screws.What angle countersink do I need for machine screws? Metric countersunk screws (ISO 7046 / DIN 965) use 90° included head angle — pair with a 90° countersink bit. Imperial countersunk screws (UNC/UNF #10-24, 1/4"-20 etc.) use 82° head angle — pair with an 82° countersink bit. Using the wrong angle leaves a gap under the head that concentrates stress and can crack surrounding material or let the head sit proud. Can I make a counterbore with an end mill? Yes — a flat-ended end mill in a milling machine or drill press produces a counterbore-equivalent flat-bottomed recess. This is common practice when a matching piloted counterbore is not available or a non-standard diameter is required. On CNC, an end mill with helical entry gives a cleaner result than plunging. Note: an end mill does not have a pilot, so hole position accuracy depends on machine setup, not tool geometry. Do I need to lubricate when counterboring? Yes for steel, stainless steel, and cast iron — cutting fluid (Tap Magic or similar) extends tool life significantly and produces a cleaner bore. Aluminium can be run dry or with a light lubricant such as WD-40 or kerosene. For piloted counterbores in production use, flood coolant is standard. Never dry-cut stainless — it work-hardens rapidly and destroys the cutter. What speed and feed should I use for counterboring? Slow speed, steady feed. In mild steel, run HSS counterbores at about 30% of the equivalent drill RPM (e.g. if a 13mm drill runs at 550 RPM in steel, run a 13mm HSS counterbore at 150-200 RPM). Feed steadily — do not peck-drill. Solid carbide counterbores run 2-3× faster. Always confirm speed and feed against the manufacturer's spec for the exact tool you have. Where can I buy counterbore bits in Australia? AIMS Industrial stocks HSS and carbide counterbore bits from Sutton Tools, Bordo, and other major brands, along with matching pilot pins and Weldon-shank arbors. Contact the AIMS trade team for size, material, and quantity — most standard metric and imperial sizes are held in stock at the Milperra warehouse.
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