Thread sealant leaks are rarely the product's fault. When a threaded pipe joint fails, the usual causes are wrong product selection, inadequate surface preparation, or the wrong sealant for the thread form. Getting this right on hydraulic and pneumatic systems — where a leak is a safety event, not just a maintenance issue — requires knowing not just which Loctite thread sealant to use, but why.
This guide covers every Loctite thread sealant product AIMS stocks for Australian industrial maintenance — 542, 565, 567, 569, 577, 5770, 5331 and Loctite 55 cord — with selection guidance by application type, pressure rating, media, and thread material.
Thread Sealant vs PTFE Tape vs Pipe Dope: What's the Difference?
Before choosing a Loctite thread sealant, it's worth knowing where it sits in the tool kit.
PTFE tape (Teflon tape) is applied by wrapping tape around the male thread before assembly. It reduces friction and fills thread form gaps. It works reasonably well on low-pressure water and gas connections. It doesn't adhere to the metal surfaces, doesn't resist vibration, and can shred into the system — a concern in any application with filters, valves, or precision equipment downstream.
Pipe dope (traditional jointing compound) is applied to threads as a paste. It works on most fluids, but doesn't cure to a hard bond and can be squeezed into the system. In hydraulic applications, dope contaminating the fluid is a serious problem.
Loctite anaerobic thread sealant cures between the metal threads, filling the thread form completely to form a leak-free seal. It doesn't shred, doesn't contaminate the system, resists vibration and pressure cycling, and is rated to specific pressure and temperature limits. It's the correct choice for hydraulic, pneumatic, gas, and industrial piping systems.
Loctite 55 cord is a PTFE-impregnated thread seal cord — a modern equivalent to PTFE tape but more flexible, reusable in staging, and rated for a wider range of media. It's the right choice where an anaerobic sealant isn't suitable (non-metal threads, oxygen systems) or where immediate pressurisation is needed.
How Loctite Thread Sealants Work
Loctite thread sealants are anaerobic adhesives. They remain liquid while exposed to air during application, then cure when confined between the male and female threads — triggered by the absence of oxygen and the presence of metal ions in the thread surface.
The cured seal fills the helix gap in the thread form completely. Unlike tape or paste, there's no void for fluid to find a path through. The seal also bonds to both thread surfaces, which gives it vibration resistance that tape simply cannot match.
Cure times range from 15 minutes (handling strength) to 24 hours (full pressure-rated strength). The product cannot withstand full system pressure until full cure is achieved — this is the most common cause of "the fitting leaked after I reassembled it."
Loctite Thread Sealant Comparison Chart
⚠️ Verify before specifying: Specifications below are sourced from Loctite published technical data and AIMS's own product data sheets. Always confirm against the current TDS for the specific product, and against the system's applicable Australian Standard or engineering specification, before commissioning.
| Grade | Colour | Strength | Thread Type | Max Temp | Fixture Time | Key Property |
|---|---|---|---|---|---|---|
| 542 | Red/brown | Low-medium | Fine hydraulic (M10–M30) | 150°C | 15 min | Fine thread specialist |
| 565 | White | See TDS | Tapered metal pipe threads | See TDS | Immediate low-pressure seal | Instant seal for air pressure testing |
| 567 | White | Low | BSP/NPT, stainless steel | 150°C | 15–30 min | Designed for SS threads |
| 569 | Not specified | High | Fine hydraulic metal pipes | See TDS | Immediate low-pressure seal | Hydraulic-grade, high strength |
| 577 | Yellow | Medium | BSP/NPT coarse | 150°C | 15 min | General industrial standard |
| 5770 | Brown | High-strength | BSP/NPT, high-pressure | 200°C | 30 min | High pressure/temp applications |
| 5331 | Not specified | Low | Plastic and metal water/drainage pipe | 150°C | See TDS | DVGW certified, plastic-to-plastic and plastic-to-metal |
| 55 | White/grey | N/A (cord) | Most thread forms | 130°C | Immediate (no cure) | No cure required, reusable staging |
Loctite 577 — The Standard for Industrial BSP and NPT
Colour: Yellow. Thread type: Coarse tapered and parallel threads — BSP (R, G) and NPT. Service temp: –55°C to 150°C. Fixture time: 15 minutes handling strength, 24 hours full cure.
Loctite 577 is the most widely used thread sealant in Australian industrial maintenance. It's the default for hydraulic systems, compressed air lines, pneumatic systems, and general-purpose industrial piping — wherever BSP or NPT connections need sealing.
577 is appropriate for:
- Hydraulic system connections: pressure ports, return lines, case drain ports, manifold connections
- Compressed air and pneumatic systems
- Water, steam, and general industrial fluid systems
- Gear oil and lubrication system connections
- Refrigeration connections (check specific refrigerant compatibility)
577 is not appropriate for:
- Stainless steel fittings without activator (passive metal — cure inhibition applies) → use 567 instead
- Very fine metric hydraulic threads (M10 and below) → 542 is better suited
- Oxygen systems → 577 is not oxygen-service rated; use 55 cord or a dedicated oxygen-compatible product
- High-pressure hydraulic above ~150 bar → consider 5770
- Plastic threads carrying water or drainage → 577 can stress-crack polycarbonate and some other plastics; use the dedicated Loctite 5331 plastic pipe sealant instead
Application note: 577 is yellow. This matters in maintenance environments — the colour confirms thread sealant has been applied and distinguishes it from threadlocker (which is also applied to threaded connections but serves a different purpose).
Shop Loctite 577 — see also the dedicated Loctite 577 guide.
Loctite 567 — For Stainless Steel Threads
Colour: White. Strength: Low. Thread type: BSP, NPT, and metric threads on stainless steel. Service temp: –55°C to 150°C. Fixture time: 15–30 minutes handling strength, 24 hours full cure.
567 is formulated specifically for stainless steel threads. The passive oxide layer on stainless steel that inhibits standard anaerobic cure is addressed in 567's formulation — it cures reliably on stainless without requiring Activator N. On AIMS's own product listing, 567 is rated Low Strength — a deliberate design choice for a sealant that needs to remain serviceable on instrumentation and stainless fittings that may be disturbed during maintenance, not an indication it seals poorly.
This makes it the first choice for:
- Stainless steel hydraulic fittings and manifolds
- Food and beverage processing pipework (stainless) — confirm grade suitability with Loctite for food-contact applications
- Chemical plant where stainless is specified for corrosion resistance
- Marine and offshore stainless steel pipework
567 vs 577 on stainless: If you use 577 on stainless threads, you need to apply 7649 Activator N first and allow it to flash off. 567 eliminates that step. In high-volume or rapid-assembly environments, 567 saves meaningful time. For occasional use, 577 plus activator works, but 567 is the cleaner solution.
Loctite 542 — Fine Hydraulic Thread Specialist
Colour: Red-brown. Thread type: Fine metric threads M10–M30, SAE straight thread O-ring boss (without O-ring). Service temp: –55°C to 150°C. Fixture time: 15 minutes handling strength, 24 hours full cure.
542 is the right product for fine-thread hydraulic connections — the type found on hydraulic manifolds, cartridge valves, SAE ports, and metric hydraulic fittings in modern mobile and industrial hydraulic systems.
Coarse thread products like 577 don't seal fine threads reliably — the larger thread pitch and smaller thread engagement depth mean the product doesn't fill consistently. 542 is formulated for fine thread pitch geometry.
Use 542 for:
- SAE straight thread boss connections (without O-ring seal — if an O-ring is present, thread sealant is not required and may cause O-ring damage)
- Fine metric hydraulic ports on machinery, cylinders, and valves
- Instrument connections on hydraulic systems
- Fuel injection system fittings (check fuel compatibility in the TDS)
542 is not for: BSP or NPT connections — use 577 or 5770 for these.
Loctite 565 — PST Instant-Seal Pipe Sealant
565 is a white, one-part pipe sealant built for an instant seal on tapered metal pipe threads — AIMS's own product data describes it as suited to air pressure testing, where the joint needs to hold pressure immediately rather than after a cure period. A specific strength tier and temperature rating weren't published on AIMS's product listing for 565 — confirm both against the current Loctite TDS before specifying it for a pressure-critical or high-temperature system.
Use 565 for:
- Tapered metal pipe threads needing an immediate low-pressure seal, ahead of full anaerobic cure
- Air pressure testing of assembled pipework, where waiting 24 hours for full cure isn't practical
What 565 won't do: It isn't positioned as a high-pressure, high-temperature product the way 5770 is — for hydraulic systems above 577's normal operating envelope, 5770 remains the better-documented choice.
Loctite 569 — Hydraulic High-Strength Thread Sealant
569 is a hydraulic-grade thread sealant built for fine threaded metal pipes and fittings, rated High Strength on AIMS's own product listing. It's a low-to-medium viscosity product that cures anaerobically when confined between close-fitting metal surfaces, and — like 565 — is positioned for an immediate low-pressure seal ahead of full cure.
Use 569 for:
- Fine threaded hydraulic pipe and fitting connections where higher bond strength than 542 is wanted
- Assemblies where resisting shock and vibration loosening matters as much as the fluid seal itself
569 vs 542: Both target fine hydraulic threads. 569 is the higher-strength option where the joint won't be disturbed again; 542 remains the better-documented general choice for routine fine-thread hydraulic work. Confirm exact temperature rating and disassembly requirements against the current TDS before specifying either for a critical joint.
Loctite 5770 — High-Pressure High-Temperature Applications
Colour: Brown. Thread type: BSP, NPT, and metric. Service temp: –55°C to 200°C. Fixture time: 30 minutes handling strength, 24 hours full cure.
5770 fills the gap above 577 for applications where temperature or pressure exceeds 577's comfortable range. At 200°C service temperature and rated for higher-pressure applications, it's used in:
- High-pressure hydraulic systems (above ~150 bar where additional safety margin is wanted)
- Steam system connections
- Thermal oil and hot-fluid system pipework
- Compressed gas at elevated pressure
- Industrial gas systems
Cure note: 5770 has a longer fixture time than 577. The additional chemical stability that gives it higher temperature resistance also slows initial cure. Don't pressure-test until 24 hours at temperature.
Loctite 5331 — Plastic Pipe Sealant
5331 is the dedicated product for plastic pipe threads — the gap left when 577, 567, 542, 569 and 5770 are all metal-thread products that risk stress-cracking plastic fittings. On AIMS's own product data, 5331 is a low-strength, medium-viscosity sealant rated –55°C to 150°C with a 1.5 N·m breakaway torque, DVGW certified for hot and cold water systems, and designed for plastic-to-plastic and plastic-to-metal fittings on industrial and agricultural water pipe and drainage systems.
Use 5331 for:
- Plastic-to-plastic and plastic-to-metal threaded fittings carrying hot or cold water
- Agricultural and industrial plastic pipe and drainage systems
- Any plastic-threaded water connection where 577 or another anaerobic metal-thread sealant risks stress cracking
5331 vs Loctite 55 cord on plastic threads: For water and drainage systems specifically, 5331 is the more targeted product — it's DVGW certified for the purpose and formulated for the plastic-to-plastic/plastic-to-metal interface. Loctite 55 cord remains the right choice for plastic threads outside water service — gas connections, oxygen systems, or any joint needing an immediate seal with no cure time at all.
Loctite 55 — Thread Seal Cord
Type: PTFE-impregnated thread seal cord. Thread type: Most thread forms including BSP, NPT, metric. Service temp: up to 130°C. Immediate service: Yes — no cure time required.
Loctite 55 is a modern alternative to PTFE tape. It's a continuous PTFE cord wound onto a spool, applied by winding around the male thread before assembly. Unlike tape, it doesn't need to be cut — it cuts cleanly on assembly, doesn't bunch or stretch, and excess cord is rewound on the spool.
Use Loctite 55 when:
- The fitting needs to be pressurised immediately after assembly (no cure time)
- The thread is non-metallic and outside water/drainage service (nylon, brass in plastic body) where anaerobic sealants may cause stress cracking — for plastic water and drainage pipe specifically, 5331 is the more targeted choice
- Oxygen service — 55 is suitable for oxygen systems; most anaerobic sealants are not
- Potable water applications — 55 is NSF 61 certified for potable water
- Gas connections — 55 is approved for natural gas, LPG, and other fuel gases (check applicable Australian Standard for your specific application)
- Field maintenance where the joint may need to be remade during assembly
55 vs PTFE tape: 55 is cleaner to apply, doesn't tear or bunch, and rewinds onto the spool — no waste, no shredding into the system. For most BSP/NPT connections, 55 is a superior product to tape. However, it doesn't provide the vibration resistance or bond strength of anaerobic sealants — for vibrating machinery, anaerobic sealants remain the better choice.
Media Compatibility Quick Reference
This is a general guide only — always verify against the specific product TDS for your media.
| Media | 542 | 565 | 567 | 569 | 577 | 5770 | 5331 | 55 |
|---|---|---|---|---|---|---|---|---|
| Hydraulic oil | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | – | ✓ |
| Compressed air | ✓ | ✓ | ✓ | ✓ | ✓ | ✓ | – | ✓ |
| Potable / hot & cold water | – | – | – | – | – | – | ✓ (DVGW) | ✓ (NSF 61) |
| Natural gas | – | – | – | – | – | – | – | ✓ |
| Diesel / fuel | ✓* | ✓* | ✓* | ✓* | ✓* | ✓* | – | ✓ |
| Steam | – | – | – | – | – | ✓ | – | ✓ |
| Stainless threads | + activator | + activator | ✓ (designed for) | + activator | + activator | + activator | – | ✓ |
| Plastic pipe (water/drainage) | ✗ | ✗ | ✗ | ✗ | ✗ | ✗ | ✓ (designed for) | ✓ (non-water) |
| Oxygen | ✗ | ✗ | ✗ | ✗ | ✗ | ✗ | ✗ | ✓ |
*Confirm fuel compatibility in current product TDS — formulations vary.
✓ = Compatible | ✗ = Not suitable | – = Not primary use, check TDS | + activator = suitable with activator
How to Apply Loctite Thread Sealant
What you need:
- Selected Loctite thread sealant
- Loctite 7063 Cleaner/Degreaser
- Loctite 7649 Activator N (for stainless steel with 577, 542, 569, 565, or 5770)
- Clean lint-free cloths
- Calibrated torque wrench
Procedure:
- Inspect and clean threads. Check threads for damage, cross-threading, or significant corrosion. Any thread damage will prevent consistent sealing. Clean both male and female threads with Loctite 7063 and allow to fully dry.
- Apply activator if required. For stainless threads (using 577, 542, 569, 565, or 5770): apply 7649 to both parts, allow 5–10 minutes to flash off. For 567: no activator needed on stainless.
- Apply thread sealant to male threads. Apply a bead of sealant around the first few threads of the male fitting. For tapered threads (BSP/NPT), apply sealant along the threaded section that will be engaged. Don't apply to the very first thread — some will wipe off as the fitting engages and this keeps the sealant in the effective sealing zone. For plastic threads, use 5331 (water/drainage) rather than a metal-thread anaerobic product.
- Assemble immediately. Engage the fitting by hand first to confirm thread engagement, then torque to specification. Don't overtorque — thread sealant is not a substitute for correct make-up torque.
- Do not rotate after initial torque. Unlike PTFE tape, where you can unscrew slightly to align a fitting face, Loctite thread sealants begin curing as soon as the threads close. If you need alignment, factor this into your installation technique — align before full torque, not after.
- Allow cure before pressurisation. Handling strength: 15–30 minutes (product dependent; 565 and 569 are positioned for an immediate low-pressure seal ahead of this). Full pressure-rated cure: 24 hours at 22°C. Do not pressure-test the system until full cure is achieved. At temperatures below 10°C, extend cure time to 48 hours.
Common mistakes:
- Pressurising before full cure. This is the number one cause of sealing failures after re-assembly. The product passes a low-pressure test at 15 minutes but fails at full system pressure because it hasn't reached full strength.
- Not cleaning stainless threads. Passive metal inhibition is real. A thread sealant that cures fine on carbon steel will cure poorly or not at all on stainless without either 567 or 7649 activator.
- Over-applying product. Excess sealant squeezes into the system and can block filters, damage seals, or contaminate precision components. A thin bead on the engaged thread area is sufficient.
- Re-torquing a cooled fitting. If you need to re-torque after the product has begun to cure, remove the fitting completely, clean with 7063, and re-apply fresh sealant. Partial cure followed by re-torque gives inconsistent and unreliable sealing.
- Using a metal-thread sealant on plastic pipe. 577, 567, 542, 569, 565 and 5770 are all formulated for metal threads and can stress-crack plastic fittings. Use 5331 for plastic water/drainage threads, or 55 cord for other plastic-thread applications.
Removing Loctite Thread Sealant
542, 565, 567, 569, 577: Once fully cured, most connections can be broken with a pipe wrench or appropriate spanner. The sealant breaks adhesively within the thread interface. Clean threads with Loctite 7063 and a wire brush before re-sealing.
5770: May require moderate heat (up to 150°C) to soften before disconnection in larger thread sizes.
5331: Its low-strength formulation is designed for serviceable plastic and metal water fittings — standard hand-tool disassembly is expected without heat.
After removal, re-apply fresh sealant — do not re-assemble onto old cured product.
Thread Sealant and Australian Standards
Loctite thread sealants are used across Australian industry in applications governed by:
- AS 4041 — Pressure piping
- AS/NZS 3788 — Pressure equipment inspection
- AS 1210 — Pressure vessels
- AS/NZS 1596 — LP gas storage and handling
Thread sealant selection for systems falling under these standards should be confirmed against the specific standard requirements and the product TDS. AIMS Industrial can assist with specifying the correct product for your application — contact us with your system details.
Frequently Asked Questions
What is the difference between Loctite 567 and 577?
577 is the general-purpose industrial thread sealant for BSP and NPT threads on carbon steel fittings, rated Medium Strength. 567 is formulated specifically for stainless steel threads and rated Low Strength — it cures reliably on passive stainless surfaces without requiring a primer, and the lower strength rating keeps stainless and instrumentation fittings serviceable. On carbon steel, 577 is the better-suited product. On stainless steel, 567 is the cleaner solution; 577 works but requires Loctite 7649 Activator N.
Can Loctite thread sealant be used on gas fittings?
Loctite 55 cord is rated for natural gas, LPG, and other fuel gas applications. Most anaerobic thread sealants (577, 567, 542, 569, 565, 5770) are not explicitly gas-rated unless specified in the product TDS. For gas connections, use Loctite 55 cord or confirm the specific product is approved for the gas in question. Never use PTFE tape on gas connections — Loctite 55 is the superior product for this application.
How long does Loctite thread sealant take to cure?
Handling strength (light assembly loads): 15–30 minutes depending on grade — 565 and 569 are positioned for an immediate low-pressure seal ahead of this. Full cure for pressure-rated sealing: 24 hours at 22°C. Below 10°C ambient temperature, extend to 48 hours. Do not pressure-test the system until full cure — this is the most common cause of sealing failures after Loctite application.
Can Loctite thread sealant be used on plastic threads?
Most anaerobic thread sealants (577, 567, 542, 569, 565, 5770) are not suitable for plastic threads — they can cause stress cracking on polycarbonate, ABS, and other plastics. For plastic-to-plastic and plastic-to-metal fittings on hot or cold water and drainage systems, Loctite 5331 is the dedicated, DVGW-certified product. For plastic threads outside water service, Loctite 55 cord is the safer choice. Always check the product TDS for plastic compatibility before use.
What Loctite product should I use on plastic water pipe?
Loctite 5331 is the purpose-built product for plastic and metal fittings carrying hot or cold water — it's DVGW certified, rated –55°C to 150°C, and formulated specifically for plastic-to-plastic and plastic-to-metal joints on industrial and agricultural water and drainage systems. It's a more targeted answer than 55 cord for this specific application, though 55 remains suitable where the system isn't water-specific.
Is Loctite 577 suitable for steam?
577 is rated to 150°C service temperature. Low-pressure steam below 150°C is generally within its range, but confirm the maximum temperature and pressure for your specific system. For higher-temperature steam applications, use Loctite 5770 (rated to 200°C). For saturated steam systems, verify the temperature at the operating pressure against the product's rating.
Do I need to use Loctite 7649 Activator before applying 577?
On carbon steel and brass threads, no — 577 cures without activator. On stainless steel threads, yes — stainless is a passive metal that inhibits anaerobic cure. Either apply 7649 Activator N before 577, or switch to Loctite 567 which is formulated to cure on stainless without activator.
Can I reuse a thread connection sealed with Loctite?
Yes. Remove the fitting, clean both threads with Loctite 7063 and a thread chaser or wire brush, allow to dry, and apply fresh sealant before reassembly. Do not reassemble on old cured product.
What's the difference between Loctite thread sealant and Loctite threadlocker?
Both are anaerobic adhesives applied to threaded connections, but they do different jobs. Thread sealant seals against fluid leakage through the thread helix — it fills the gap in the thread form to create a pressure-tight seal. Threadlocker creates a locking force that resists vibration-induced loosening of the fastener. Some applications need both (a hydraulic cylinder port bolt that also locks the fastener), but they are applied to different surfaces and serve different functions.
Is Loctite 577 safe for potable water?
577 is not NSF 61 certified for potable water. For metal potable water connections, use Loctite 55 cord, which is NSF 61 certified. For plastic potable water fittings, Loctite 5331 is DVGW certified. Check the current Loctite documentation as certifications may be updated — do not rely on historical certification status for current installations.
What is the maximum pressure Loctite 577 can seal?
This is system-dependent and varies by thread size, thread form, and application. Loctite's published data indicates pressure ratings in the range of 150–200 bar for typical BSP/NPT connections, but the correct approach is to confirm against the current TDS and the engineering specification for your system. For high-pressure applications (above 200 bar), consult AIMS and reference Loctite's engineering data directly.
What is Loctite 5331 used for?
5331 is a low-strength, DVGW-certified plastic pipe sealant for locking and sealing plastic-to-plastic and plastic-to-metal fittings carrying hot or cold water — typically industrial and agricultural plastic water pipe and drainage systems. Its breakaway torque is 1.5 N·m and it's rated –55°C to 150°C, deliberately low-strength so plastic fittings remain serviceable.
What is Loctite 569 used for?
569 is a hydraulic-grade, high-strength thread sealant for fine threaded metal pipes and fittings — used where a stronger bond than 542 is wanted on fine hydraulic threads, and where an immediate low-pressure seal ahead of full cure is useful, such as during pressure testing.
What is Loctite 565 used for?
565 is a white, one-part pipe sealant for tapered metal pipe threads, built to give an instant seal suited to air pressure testing — useful where a joint needs to hold pressure straight away rather than waiting for a full anaerobic cure.
Which Loctite thread sealant is strongest?
Among grades with a published strength tier, 5770 is rated high-strength and is also the highest-temperature product in the range (200°C), followed by 569 (high strength, fine hydraulic threads). 577 and 542 sit at medium strength; 567 and 5331 are deliberately low-strength for serviceability on stainless and plastic fittings respectively.
People Also Ask — Loctite Thread Sealant
Q: What are the differences between LOCTITE 567 and 577 thread sealants?
567 is formulated for stainless steel and rated Low Strength; 577 is the general-purpose carbon steel product rated Medium Strength. 567 needs no activator on stainless; 577 does.
Q: Can LOCTITE be used as a thread sealer?
Yes — Loctite's anaerobic thread sealant range (542, 565, 567, 569, 577, 5770) is designed specifically to seal threaded metal pipe fittings against fluid and gas leakage, curing between the threads to fill the helix gap completely.
Q: What's the difference between thread lock and thread sealant?
Threadlocker resists vibration-induced loosening of a fastener. Thread sealant seals a threaded pipe joint against fluid or gas leakage. Both are anaerobic Loctite products applied to threads, but they solve different problems.
Q: Is LOCTITE stronger than JB Weld?
They're different product categories rather than directly comparable on one strength scale. Loctite thread sealants and threadlockers are engineered anaerobic adhesives for threaded joints with published shear and breakaway figures; JB Weld is a general-purpose epoxy. For a threaded pipe or fastener application, the correctly specified Loctite product is the appropriate choice rather than a general epoxy.
Related Guides
- The Complete Loctite Application Guide — overview of all Loctite product families
- Loctite 577 Guide — dedicated guide to the most commonly used thread sealant in Australian industry
- Loctite Threadlocker Guide — for locking threaded fasteners in the same systems
- Loctite Retaining Compound Guide — bearing and cylindrical assembly retention
All technical specifications should be verified against the current Loctite Technical Data Sheet for the specific product before use in pressure systems, gas pipework, or safety-critical applications. For applications governed by Australian Standards, consult with a qualified engineer. Contact the AIMS Industrial team if you need help specifying the right thread sealant for your system.