Product Guides

Hydraulic Fittings Guide

Hydraulic fittings are where most hydraulic system problems start. A fitting is a small component, but when it is wrong — wrong thread type, wrong sealing method, wrong torque — the result is a leak that at best wastes fluid and at worst fails catastrophically under pressure. The frustration of identifying an unknown fitting, sourcing the right replacement, and getting it sealed correctly is one of the most common complaints in any workshop that services mixed-origin machinery. Australia runs a genuine mix of hydraulic standards. Older plant, process equipment, and British-derived machinery typically uses BSP (British Standard Pipe). American tractors and mobile equipment use JIC. New OEM equipment from European and global manufacturers increasingly specifies ORFS (O-ring face seal). Add DIN metric fittings on German and Japanese equipment, and NPT (National Pipe Taper) on some North American-origin components, and the average Aussie workshop is dealing with four or five incompatible thread systems on a given day. This guide covers every major hydraulic fitting type used in Australian industry and agriculture: how each one seals, how to identify them with basic tools, the size reference charts you need in the workshop, and the common mistakes that cause most hydraulic leaks. Read the identification section carefully — it is the one section that will save you the most time and money. Contents What are hydraulic fittings? The main fitting standards BSP fittings: BSPP vs BSPT JIC fittings (37° flare) ORFS fittings (O-ring face seal) ORB fittings (O-ring boss) NPT — the American thread DIN metric fittings 5-step fitting identification guide BSP thread size reference chart JIC size chart Reusable vs crimped fittings Common mistakes that cause leaks Frequently asked questions For more engineering reference charts and selection tables, see our Engineering Reference Charts hub — covering fasteners, bearings, lubrication, measuring, welding and Australian standards. Comprehensive thread cross-reference chart — Quick Reference Common nominal sizes mapped across all major standards. Sizes match physically when in the same row even though designations differ. Nominal BSP / ISO 228 (G) / AS 1722 BSP Tapered / ISO 7-1 (R) NPT / ASME B1.20.1 JIS PT Pitch (mm) 1/8" G 1/8 (28 TPI) R 1/8 (28 TPI) 1/8 NPT (27 TPI) PT 1/8 BSP: 0.907 / NPT: 0.941 1/4" G 1/4 (19 TPI) R 1/4 (19 TPI) 1/4 NPT (18 TPI) PT 1/4 BSP: 1.337 / NPT: 1.411 3/8" G 3/8 (19 TPI) R 3/8 (19 TPI) 3/8 NPT (18 TPI) PT 3/8 BSP: 1.337 / NPT: 1.411 1/2" G 1/2 (14 TPI) R 1/2 (14 TPI) 1/2 NPT (14 TPI) PT 1/2 BSP: 1.814 / NPT: 1.814 3/4" G 3/4 (14 TPI) R 3/4 (14 TPI) 3/4 NPT (14 TPI) PT 3/4 BSP: 1.814 / NPT: 1.814 1" G 1 (11 TPI) R 1 (11 TPI) 1 NPT (11.5 TPI) PT 1 BSP: 2.309 / NPT: 2.209 1-1/4" G 1 1/4 (11 TPI) R 1 1/4 (11 TPI) 1-1/4 NPT (11.5 TPI) PT 1 1/4 BSP: 2.309 / NPT: 2.209 1-1/2" G 1 1/2 (11 TPI) R 1 1/2 (11 TPI) 1-1/2 NPT (11.5 TPI) PT 1 1/2 BSP: 2.309 / NPT: 2.209 2" G 2 (11 TPI) R 2 (11 TPI) 2 NPT (11.5 TPI) PT 2 BSP: 2.309 / NPT: 2.209 What are hydraulic fittings? A hydraulic fitting is a connector that joins hoses, tubes, pipes, valves, cylinders, and pumps in a hydraulic system. Unlike water plumbing, hydraulic systems operate at extreme pressures — commonly 150–300 bar (2,200–4,350 psi) in mobile equipment, and up to 700 bar (10,000 psi) in specialist industrial applications. At these pressures, a poorly sealed fitting does not drip — it sprays, and hydraulic fluid injection injuries are a genuine industrial safety hazard. Fittings must accomplish two things simultaneously: make a secure mechanical connection that resists pressure and vibration, and create a leak-free seal. The sealing method — thread taper, cone-to-cone metal contact, O-ring compression, or bonded seal — is what differentiates the major fitting standards. Understanding how a fitting seals is the foundation for selecting, installing, and troubleshooting correctly. The main fitting standards at a glance Before going into detail on each type, here is the landscape in a single table. Standard Origin Thread type Sealing method Common in Australia BSPP (BSP parallel) UK/Commonwealth Parallel, 55° thread form Bonded seal (Dowty washer) or O-ring Process plant, older equipment, fluid power BSPT (BSP tapered) UK/Commonwealth Tapered, 55° thread form Thread taper + thread sealant Plumbing, older hydraulic ports JIC (SAE 37°) USA Straight UNF 37° metal-to-metal flare seat American tractors, mobile plant, agriculture ORFS USA / Global OEM Straight UNF O-ring on flat face New OEM equipment, mining, construction ORB (SAE O-ring boss) USA Straight UNF O-ring at base of male thread Valve and port connections on American equipment NPT USA Tapered, 60° thread form Thread taper + PTFE tape or thread sealant Some North American plant; uncommon in Aus hydraulics DIN metric Germany / Europe Metric parallel or tapered Varies: cone seat, O-ring, or bonded seal European machinery, some Japanese equipment BSP fittings: BSPP vs BSPT BSP (British Standard Pipe) is the dominant fitting standard across most of Australia's installed base of process plant, hydraulic power units, and older British-derived mobile equipment. The BSP family splits into two fundamentally different thread types that share the same thread pitch and diameter but seal in completely different ways. Confusing them is one of the most common causes of hydraulic leaks. BSPP — British Standard Pipe Parallel BSPP (also designated G-thread) has a constant diameter from end to end — the threads are parallel, not tapered. Because the threads do not wedge together, they cannot seal by thread engagement alone. BSPP seals using a bonded seal (Dowty washer) or an O-ring that seats against a flat machined face on the port. The bonded seal is a rubber-bonded metal washer — a thin steel ring with a rubber seal element moulded to its inner face. When the male fitting is tightened, the bonded seal compresses between the machined face of the male fitting and the port face, creating the hydraulic seal. The seal is in the washer, not in the threads. This is critical: if the bonded seal is lost during disassembly (they often are — they fall off and get swept up), the reinstalled fitting will appear to be correctly tightened but will leak immediately under pressure. BSPP ports cannot be sealed by thread engagement or PTFE tape. Always carry spare bonded seals in the sizes you work with. BSPP is by far the more common BSP variant in modern hydraulic systems. Most hydraulic valves, cylinders, pumps, and fittings with BSP ports use BSPP (G-thread) ports. BSPT — British Standard Pipe Tapered BSPT (also designated R-thread) has a 1:16 taper — the thread diameter gradually decreases toward the end of the fitting. When tightened, the tapered thread wedges into the port, creating mechanical interference. BSPT seals by this wedging action, typically assisted by a thread sealant (PTFE tape is sometimes used, though hydraulic-grade anaerobic thread sealant is preferred for hydraulic applications). BSPT is less common in modern hydraulic components but is still found in older equipment, some plumbing connections on hydraulic power units, and as gauge ports on some cylinders and manifolds. How to tell BSPP from BSPT Hold the fitting with the threaded end pointing toward you. Using the parallel jaws of a vernier calliper, measure the thread diameter at two points: near the tip of the thread and further back toward the fitting body. If the two measurements are the same (within 0.1 mm), the thread is parallel — BSPP. If the measurement near the tip is noticeably smaller, the thread is tapered — BSPT. Do not rely on visual inspection alone; the taper is subtle and easy to miss by eye. JIC fittings (37° flare) JIC (Joint Industry Council) fittings use a 37° cone seat as the sealing surface. The male fitting has a 37° flare machined onto its nose. When assembled, the 37° cone on the male seats against a matching 37° seat in the female swivel nut, creating a metal-to-metal seal under clamping force. JIC is the standard American hydraulic fitting and is found on most American-made tractors, construction equipment, agricultural machinery, and industrial hydraulic systems. In Australia, JIC is common on John Deere, Case, New Holland, Caterpillar, and similar American-origin equipment. Key characteristics: Thread: UNF (Unified National Fine) straight thread — the threads do not seal; the cone does. Pressure rating: Up to 690 bar (10,000 psi) depending on size and material. Identification: The 37° cone on the male fitting nose is the giveaway. Look for the angled taper on the male end and the matching flared seat inside the female. Reassembly tolerance: JIC can be assembled and disassembled multiple times. The metal-to-metal seat does work-harden over many cycles, so inspect the seating surface for pitting or scoring on older fittings. JIC vs AN fittings AN (Army-Navy) fittings use the same 37° cone geometry as JIC and are dimensionally interchangeable in most sizes. The difference is the standard under which they are manufactured: AN fittings are to aerospace specifications (tighter tolerances, higher material grades), while JIC is the industrial equivalent. In a hydraulic system, JIC and AN fittings of the same nominal size will assemble and seal together correctly. Do not over-think this distinction — if the 37° cone fits, it works. ORFS fittings (O-ring face seal) ORFS (O-ring face seal, also known as SAE face seal or flat-face) is increasingly specified on new OEM equipment worldwide and is now common on mining, construction, and agricultural machinery manufactured in the last 15–20 years. The male ORFS fitting has a flat machined face with a groove containing an O-ring. The female fitting (or port) has a matching flat face. When assembled, the O-ring is compressed between the two flat faces, creating the seal. The UNF thread provides clamping force only — the O-ring does all the sealing work. Why ORFS is becoming the preferred standard on new equipment: Leak resistance: The O-ring seal is far more tolerant of vibration, thermal cycling, and port imperfections than a metal-to-metal cone seat. ORFS has a significantly lower leak rate in service than JIC. Flat face prevents contamination: The flat face design (no recessed cavity) makes the fitting easier to clean and less likely to trap contamination when disconnected. Over-torque tolerance: ORFS can withstand significant over-tightening without damage to the sealing surface. JIC cone seats can be damaged by over-torque. Visual identification: The flat face with a visible O-ring in a groove is unmistakable once you know what you are looking for. The main limitation of ORFS: the O-ring must be in good condition. A nicked, deteriorated, or missing O-ring will leak immediately. Always inspect or replace the O-ring when reassembling ORFS connections. ORB fittings (O-ring boss) ORB (O-ring boss, also called SAE O-ring boss or SAE straight thread O-ring) is a port connection type commonly found on valves, cylinders, and pump housings on American-made hydraulic equipment. It is often confused with JIC because both use UNF threads, but they seal in completely different ways. An ORB male fitting has an O-ring located at the base of the thread, between the thread body and the fitting hex. When the male fitting is threaded into the port and tightened, the O-ring is compressed against the machined chamfer at the port entrance — not against the thread faces. The seal is at the port entrance, not within the thread engagement zone. ORB ports accept adjustable-position fittings — the male fitting can be backed off and repositioned for hose routing without breaking the seal, because the O-ring at the base creates the seal regardless of rotational position. This is a significant advantage on valve banks and manifolds where fittings need to point in a specific direction. Do not confuse ORB with JIC: ORB male fittings thread straight into a port (no swivel nut). JIC uses a swivel nut assembly. If you see a male thread with an O-ring at the base threading directly into a port, it is ORB. NPT — the American thread NPT (National Pipe Taper) is the standard American tapered pipe thread. It is common on North American process equipment, compressed air systems, and some hydraulic components, but it is not the primary hydraulic fitting standard in Australia and should not be confused with BSPT. NPT has a 1:16 taper (same as BSPT) and seals by thread wedging plus PTFE tape or anaerobic thread sealant. The critical difference from BSPT is the thread form and pitch — NPT uses a 60° thread form, while BSP uses a 55° thread form. Despite having the same taper rate, NPT and BSPT threads can physically thread together in many sizes but will not seal correctly — the different thread form angles mean the contact is only partial, and the connection will leak under pressure. This is one of the most dangerous mixing errors in hydraulic maintenance. If NPT fittings appear in your hydraulic system, do not substitute BSPT and vice versa. Use adapters with the correct thread on each end. DIN metric fittings DIN (Deutsches Institut für Normung) metric fittings are common on European machinery — German, Austrian, French, and Italian equipment — and increasingly on Japanese hydraulic components. DIN fittings come in several families: DIN 2353 / ISO 8434-1 (bite-type tube fittings): The most common DIN hydraulic tube fitting — a ferrule that bites into the outer wall of a steel tube when tightened. These are compression fittings for hard hydraulic tubing, not hose fittings. DIN 7631 / DKOL (metric O-ring face seal): The DIN equivalent of ORFS — flat face with O-ring. Uses metric thread sizes. DIN 7775 (metric BSP-like): Metric parallel thread with bonded seal, functionally similar to BSPP but on metric thread sizes. When servicing European equipment, verify thread type with a metric thread gauge before sourcing replacements. DIN metric fittings are not interchangeable with BSP even where thread diameters appear similar. Pipe thread standards in depth — ISO, DIN, JIS, ASME and AS The fitting categories above (BSP, JIC, ORFS, ORB, NPT, DIN) are application-level designations. Underneath them sit the international thread standards that define the actual thread geometry — pitch, included angle, crest, root, taper rate. Understanding which standard governs which thread family makes cross-brand and cross-country compatibility decisions much easier. Standard Origin Defines AU/global use ISO 228-1 International (originally British) Parallel pipe threads — designation G (e.g. G 1/4) Europe, Asia, Australia (BSPP equivalent) ISO 7-1 International (originally British) Tapered pipe threads — designation R (external) and Rp (parallel internal) and Rc (tapered internal) Europe, Asia, Australia (BSPT equivalent) DIN 2999 Germany German equivalent of ISO 7-1 (taper); withdrawn but still referenced on older equipment European industrial equipment, legacy machinery DIN 259 Germany German equivalent of ISO 228-1 (parallel); largely superseded by ISO 228 European legacy equipment JIS B 0203 Japan Japanese pipe threads — taper external (PT), parallel internal (PS), parallel both (PF) Japanese industrial and automotive equipment ASME B1.20.1 USA NPT (National Pipe Thread) — tapered, 60° included angle, Sellers thread form North America, US-spec equipment globally ASME B1.20.3 USA NPTF (Dryseal) — interference-fit version of NPT for dry seal without compound Hydraulic and pneumatic where leak-free without sealant required AS 1722.1 Australia/NZ Australian standard for parallel pipe threads — equivalent to ISO 228-1 Australian regulatory references; gas, plumbing, hydraulics AS 1722.2 Australia/NZ Australian standard for tapered pipe threads — equivalent to ISO 7-1 Australian regulatory references; pressure systems BS 21 UK Original British pipe thread standard (now superseded by ISO 7-1 / ISO 228) Legacy UK equipment, historical reference Two practical points from the table: BSP, ISO 228 / ISO 7-1, AS 1722 and BS 21 are all the same thread family. "BSP" is the colloquial Australian and British name; ISO 228 (parallel) and ISO 7-1 (tapered) are the engineering standard references; AS 1722 is the Australian adoption. They use the same Whitworth thread form, the same 55° included angle, the same pitch table. A fitting marked "G 1/4" (ISO 228) and another marked "BSPP 1/4" mate perfectly because they're physically identical. NPT is a different thread family. ASME B1.20.1 specifies the Sellers thread form with 60° included angle, different pitches, different taper. NPT is not a regional variant of BSP — it's a fundamentally different geometry. Cross-mating BSP and NPT does not work and damages threads on first attempt (covered in detail in the next section). The G, R, Rp and Rc designations ISO 228 and ISO 7-1 use single-letter prefixes that often confuse new users. The convention: G — ISO 228 parallel thread (both internal and external). Equivalent to BSPP. Example: G 1/2 male thread mates with G 1/2 female thread, both parallel. R — ISO 7-1 tapered EXTERNAL thread. Equivalent to BSPT male. Example: R 1/2 is a male tapered fitting. Rc — ISO 7-1 tapered INTERNAL thread. Pairs with R for taper-on-taper sealing. Example: Rc 1/2 is a female tapered port. Rp — ISO 7-1 parallel INTERNAL thread. Designed to accept an R (tapered male) into a parallel female port for jam-style sealing. Less common than Rc but appears on some hydraulic and process equipment. So a port labelled Rc 1/4 on a German hydraulic valve is BSPT female. A bolt labelled G 1/2 A is a BSPP male thread. Translating between the standard designations and the colloquial BSPP/BSPT names is mostly a vocabulary exercise once you know the prefix system. Thread form geometry — Whitworth vs Sellers, and why BSP and NPT can't safely mate The fundamental incompatibility between BSP and NPT is not a regional or branding difference — it's a physical geometry difference that goes back to the 1840s and has never been reconciled. Property BSP (Whitworth form) NPT (Sellers form) Included angle 55° 60° Crest and root Rounded (radius blends crest to flank) Flat (truncated crest, flat root) Origin Sir Joseph Whitworth, England, 1841 William Sellers, USA, 1864 Taper rate (where tapered) 1:16 (BSPT and ISO 7-1) 1:16 — same taper, different form Pitch series BSP pitches (e.g. 1/2" = 14 TPI) NPT pitches (e.g. 1/2" = 14 TPI — coincidentally same) Sealing method BSPP uses bonded seal at face; BSPT uses thread-form interference + sealant NPT uses thread-form interference + sealant (PTFE tape or pipe dope) Why BSP and NPT do not mate safely, even when the diameter and TPI look the same: Different included angle. The BSP thread is a 55° "V" with rounded crests; NPT is a 60° "V" with flat crests. Force them together and only the corners of the threads touch — typically 2–3 contact points instead of full thread engagement. The connection looks tight but won't hold pressure. Different crest geometry. The flat crest of NPT against the round crest of BSP creates point contact and stress concentrations. Tightening damages the threads on both fittings — usually irreversibly. Pitch coincidences are misleading. 1/2" BSP and 1/2" NPT both happen to be 14 TPI — but the pitch is the only similarity. The thread forms don't engage. 1/4" BSP is 19 TPI; 1/4" NPT is 18 TPI — close enough to start threading but they will bind within a turn. Adapters exist for a reason. If you must connect BSP to NPT (common when integrating US-spec equipment into AU systems), use a purpose-made BSP-to-NPT adapter fitting — typically female BSP one end, male NPT the other (or vice versa). Direct mating is not an option. Practical rule for AU workshops: when in doubt about a male thread, gauge it. A BSP thread gauge (55°) and an NPT thread gauge (60°) cost under $50 each and resolve any ambiguity in seconds. Cross-threading a fitting because of a wrong assumption ruins both parts. Pipe thread standards by application — beyond hydraulics The same thread standards (BSP, NPT, ISO 228, ISO 7-1) appear across many AU industries beyond hydraulics. Each application has its own dominant standard and AU regulatory framework. Application Dominant AU standard Notes Hydraulic systems (mobile, industrial) BSP (BSPP and BSPT) ISO 228 / ISO 7-1 / AS 1722. Some imported US equipment uses NPT or JIC. Pneumatics (compressed air) BSP NPT specifically excluded from AU pneumatic standards. See AIMS Pneumatic Fittings Guide. Natural gas / LPG BSPT (taper) AS 5601 mandates tapered threads for gas service. Parallel BSPP not permitted. Plumbing (water supply, hot water) BSPT and BSPP AS 3500 series. WaterMark certification required for potable water. Drainage (sewage, stormwater) Specialty standards (push-fit, slip-on) AS 1260 for PVC-U pipe; threaded connections rare in modern drainage. Steam systems (industrial process) BSPT or NPT (per equipment origin) AS/NZS 3788 for pressure equipment. Threaded joints below DN 50 only; flanged above. Oil and gas (upstream) NPT and API API 5B and ASME B1.20.1 dominate; international standards on offshore. Compressed air (industrial scale) BSPT or BSPP AS/NZS 3788 for receivers; AS 4041 for piping. Chemical process plant Mixed (often flanged) Threaded only on small bore (DN 25 and below); flanged above. Refrigeration SAE flare (45°), some BSP SAE J512 dominates refrigeration; BSP on European HVAC equipment. Marine (water, fuel, hydraulic) BSP with corrosion-resistant materials 316 stainless or naval brass for sea water service. Mining (slurry, water, hydraulic) BSP AS 1722 references; heavy-duty fittings standard. Three points worth knowing for anyone working across multiple applications: Australian gas regulations are strict. AS 5601 (gas installations) mandates tapered threads (BSPT) for gas service. Using BSPP — which seals on a face washer, not on the thread itself — is non-compliant for natural gas and LPG. Gas fitter qualifications matter; this isn't DIY territory. Hydraulic and pneumatic look similar but differ on sealing. Most hydraulic ports are BSPP with bonded seal (face seal); most pneumatic ports are BSPT (thread seal with tape or sealant). Don't assume the standard is the same just because the thread looks the same. NPT in Australia means imported equipment. Native AU industrial design uses BSP. NPT shows up on US-imported equipment — particularly mining, agricultural, and oil & gas machinery. Plan for adapter fittings when integrating. Comprehensive thread cross-reference chart Common nominal sizes mapped across all major standards. Sizes match physically when in the same row even though designations differ. TPI = threads per inch. Nominal BSP / ISO 228 (G) / AS 1722 BSP Tapered / ISO 7-1 (R) NPT / ASME B1.20.1 JIS PT Pitch (mm) 1/8" G 1/8 (28 TPI) R 1/8 (28 TPI) 1/8 NPT (27 TPI) PT 1/8 BSP: 0.907 / NPT: 0.941 1/4" G 1/4 (19 TPI) R 1/4 (19 TPI) 1/4 NPT (18 TPI) PT 1/4 BSP: 1.337 / NPT: 1.411 3/8" G 3/8 (19 TPI) R 3/8 (19 TPI) 3/8 NPT (18 TPI) PT 3/8 BSP: 1.337 / NPT: 1.411 1/2" G 1/2 (14 TPI) R 1/2 (14 TPI) 1/2 NPT (14 TPI) PT 1/2 BSP: 1.814 / NPT: 1.814 3/4" G 3/4 (14 TPI) R 3/4 (14 TPI) 3/4 NPT (14 TPI) PT 3/4 BSP: 1.814 / NPT: 1.814 1" G 1 (11 TPI) R 1 (11 TPI) 1 NPT (11.5 TPI) PT 1 BSP: 2.309 / NPT: 2.209 1-1/4" G 1 1/4 (11 TPI) R 1 1/4 (11 TPI) 1-1/4 NPT (11.5 TPI) PT 1 1/4 BSP: 2.309 / NPT: 2.209 1-1/2" G 1 1/2 (11 TPI) R 1 1/2 (11 TPI) 1-1/2 NPT (11.5 TPI) PT 1 1/2 BSP: 2.309 / NPT: 2.209 2" G 2 (11 TPI) R 2 (11 TPI) 2 NPT (11.5 TPI) PT 2 BSP: 2.309 / NPT: 2.209 Quick read of the chart: BSP and JIS PT pitches match exactly — Japanese PT threads are physically identical to BSPT in most sizes. JIS-spec Japanese hydraulic equipment generally uses thread forms compatible with AU BSP. BSP and NPT pitches differ at most sizes. 1/4", 3/8", 1", 1-1/4", 1-1/2", 2" all have different TPI between BSP and NPT. Only 1/2" and 3/4" coincidentally share 14 TPI — but the thread form (55° vs 60°) still prevents mating. The 1/8" size is unusual — both BSP and NPT use higher-density threads for the smallest sizes. 1/8" BSP is 28 TPI; 1/8" NPT is 27 TPI. For metric thread cross-referencing in millimetres, the ISO 228 standard provides full pitch tables. The most-used sizes in AU hydraulic and pneumatic equipment span G 1/8 (10 mm OD on the male thread) through G 2 (60 mm OD). 5-step fitting identification guide When you have an unknown fitting and need to identify it, work through these five steps in order. You need: a vernier calliper, a thread pitch gauge with both imperial (TPI) and metric blades, and a reference chart (the BSP and JIC charts below will cover most Australian applications). Step 1 — Determine how the fitting seals Look at the fitting end and identify the sealing feature: Flat face with an O-ring in a groove → ORFS (or DIN face seal if metric) Angled cone on the male nose (37°) → JIC / AN O-ring at the base of the male thread (between thread and hex) → ORB Flat face, no O-ring visible, threads appear parallel → BSPP (needs bonded seal at port) No visible sealing feature — relies on thread engagement only → BSPT or NPT (tapered thread) Step 2 — Determine if threads are parallel or tapered Using the parallel jaws of a vernier calliper, measure the thread OD near the tip and again 10 mm further back. Parallel = same diameter both measurements (BSPP, JIC, ORFS, ORB). Tapered = tip diameter is smaller (BSPT, NPT). For subtle tapers, hold the fitting against a straight edge — you can usually see the taper on a tapered thread. Step 3 — Measure the thread OD Measure the outside diameter of the male thread with your calliper. Note: BSP thread sizes are nominal sizes that do not correspond to actual dimensions — a 1/2" BSP fitting has a thread OD of approximately 20.95 mm, not 12.7 mm. Use the BSP size chart below to convert your measurement to a nominal BSP size. For JIC, measure the OD and cross-reference with the JIC chart. Step 4 — Count threads per inch (TPI) Use a thread pitch gauge to count threads per inch (TPI) or pitch in mm. Place the blade against the thread at an angle and look for a perfect match. BSP threads run at specific TPI values by nominal size (see chart). JIC/ORFS/ORB use UNF thread pitches. Metric fittings will be in mm pitch. TPI combined with OD will uniquely identify the thread in almost all cases. Step 5 — Confirm against the reference chart Cross-reference your OD measurement and TPI against the BSP chart below (for BSP fittings) or JIC chart (for JIC/ORFS). For DIN metric, measure thread pitch in mm and cross-reference against a metric thread chart. If OD and TPI match a BSP size, you have BSPP or BSPT — use Step 2 to determine which. If the cone is visible, it is JIC. If the flat face + O-ring is visible, it is ORFS. Tip: bring a sample If you are still uncertain after the 5-step process, the fastest path is to take the fitting — and the mating port or fitting if possible — to a hydraulic specialist. Experienced hydraulic fitters can identify most fittings by eye and confirm with gauges in under a minute. Do not guess on a hydraulic connection: a wrong fitting that appears to thread in can fail catastrophically under pressure. BSP thread size reference chart BSP nominal sizes are historical pipe bore references, not actual thread dimensions. Use the thread OD column to match your measured fitting. BSP nominal size Thread OD (mm) TPI Common designation Typical application 1/8" 9.73 28 G1/8 (BSPP) / R1/8 (BSPT) Gauge ports, pilot ports, small instrumentation 1/4" 13.16 19 G1/4 / R1/4 Cylinder ports, small valves, air/hydraulic gauges 3/8" 16.66 19 G3/8 / R3/8 Flow control valves, cylinder ports, hose ends 1/2" 20.96 14 G1/2 / R1/2 Most common size — valves, pumps, cylinder main ports 3/4" 26.44 14 G3/4 / R3/4 Larger valve ports, pump inlets, tank connections 1" 33.25 11 G1 / R1 Pump/motor ports, large cylinder ports 1-1/4" 41.91 11 G1-1/4 / R1-1/4 Tank suction lines, large motor ports 1-1/2" 47.80 11 G1-1/2 / R1-1/2 Tank suction, return lines on larger systems 2" 59.61 11 G2 / R2 Large tank and return connections, pump suction Note on BSP designation: The G prefix = BSPP (parallel). The R prefix = BSPT (tapered). Port markings on valves and cylinders using G-thread (e.g. G1/2) indicate a BSPP parallel port requiring a bonded seal. R-thread ports require a tapered fitting with thread sealant. Both have the same thread dimensions — only the taper and sealing method differ. JIC / ORFS size chart JIC and ORFS fittings share the same UNF thread sizes. They are identified by the AN dash size system — a negative number indicating the nominal ID of the fitting in 1/16" increments. A -8 fitting has a nominal ID of 8/16" = 1/2". AN/JIC dash size Thread size (UNF) Thread OD (mm) Hose ID (approx.) Common application -4 7/16"-20 UNF 11.1 6 mm (1/4") Pilot lines, small instrumentation hoses -6 9/16"-18 UNF 14.3 10 mm (3/8") Control lines, remote valve connections -8 3/4"-16 UNF 19.1 13 mm (1/2") Most common — cylinder, motor, general hydraulic hose -10 7/8"-14 UNF 22.2 16 mm (5/8") Larger cylinder and motor lines -12 1-1/16"-12 UNF 27.0 19 mm (3/4") Pump outlet, loader valve circuits -16 1-5/16"-12 UNF 33.3 25 mm (1") Pump inlet, high-flow return lines -20 1-5/8"-12 UNF 41.3 32 mm (1-1/4") Large pump/motor ports, suction lines Telling JIC from ORFS at the same thread size: JIC has an angled 37° cone nose. ORFS has a flat face with a visible O-ring groove. Both use the same UNF thread designation (e.g. 3/4"-16 UNF for -8 size), but they are NOT interchangeable — do not mix JIC male fittings with ORFS female fittings or vice versa. Reusable vs crimped hydraulic fittings When replacing a hydraulic hose assembly, you have a choice between reusable (field-fit) fittings and crimped fittings. Each has a legitimate role. Crimped fittings A crimped fitting is permanently swaged onto the hose end using a hydraulic crimping machine. The ferrule is deformed inward, locking the fitting to the hose with a radial grip force that achieves or exceeds the hose's own pressure rating. Crimped assemblies are the industry-standard method for production hose assemblies and are specified by most OEMs. The limitations: you need a crimper (expensive, workshop-based) and a set of dies for every hose and fitting size combination. In the field, far from a workshop, you cannot make a crimped hose. Reusable fittings A reusable fitting consists of a socket that screws onto the hose OD and an insert that is driven into the hose bore. When the insert is wound in, the hose is trapped between insert and socket, creating the grip. No special tools are required beyond two spanners. The fitting can be removed, and the socket and insert can be reused on a new hose length. Reusable fittings are essential for field repairs on farm equipment, mining equipment in remote locations, and any situation where a crimper is unavailable. They are rated to the same pressure as the hose they are fitted to, provided the correct socket and insert are matched to the hose OD and wall specification. The limitations: more assembly steps, greater potential for incorrect assembly, and the seal depends on the condition of the hose end (a damaged, flared, or cut-at-angle hose end will leak). Which to choose: For permanent, shop-built hose assemblies, crimp. For field emergency repairs, for low-production applications without a crimper, or for hoses that need to be regularly disassembled (test rigs, seasonal equipment), use reusable fittings with the correct specification for the hose type. Common mistakes that cause hydraulic leaks The majority of hydraulic leaks at fittings trace back to a small number of recurring errors. Avoid these and you will eliminate most fitting-related failures. 1. Missing the bonded seal on BSPP ports The most common BSP leak in Australian workshops. The fitting is tightened correctly, the threads are correct, and it leaks from the first pressurisation. The bonded seal (Dowty washer) was lost when the fitting was removed — often falls into the machine, gets swept away with contamination, or sticks to the old fitting. Without the bonded seal, a BSPP fitting cannot seal regardless of how tightly it is torqued. Always check for and replace the bonded seal when reassembling any BSPP connection. 2. PTFE tape on BSPP ports PTFE tape is appropriate for BSPT and NPT tapered threads. It is not appropriate for BSPP parallel thread ports. Applying PTFE tape to a BSPP port prevents the bonded seal from seating correctly against the machined face, because the tape creates a compressible layer that distributes the seating force unevenly. The result is a connection that appears tight but seeps. PTFE tape on a BSPP port is not a fix — remove it, clean the faces, and fit a new bonded seal. 3. Cross-threading BSPT and NPT BSPT and NPT have the same taper rate but different thread forms (55° vs 60°). In many common sizes — particularly 1/4" and 1/2" — they will physically thread together and appear to seat correctly. Under pressure, they leak because the thread flanks do not make full contact. This is a particularly dangerous error because the connection looks right and may hold briefly before failing. Never substitute BSPT for NPT or vice versa. When in doubt, use a thread pitch gauge to confirm. 4. Confusing JIC and ORFS at the same thread size Both use UNF threads, and in some sizes the thread OD is close enough that they will thread together partially. JIC male into an ORFS female: the 37° cone contacts the flat ORFS face off-centre, creating a partial seal that fails quickly. ORFS male into a JIC female swivel: the flat face cannot create a seal in the 37° seat. Always confirm the sealing method — cone vs flat face — before assembly. 5. Over-torquing JIC fittings JIC is a metal-to-metal seal. Tightening beyond specification deforms the 37° cone, reducing the contact quality and eventually causing leak paths from cracking or distortion of the seat. JIC fittings have a specified torque (FFWR — Flats From Wrench Resistance: snug up to resistance, then turn a specified number of flats). Using torque alone without knowing the specification, or using an impact driver, will damage the cone. Use a torque wrench or the FFWR method, and inspect cone condition on reassembly of older fittings. 6. Damaged ORFS O-ring ORFS O-rings are vulnerable to nicking during assembly if the O-ring rolls out of its groove. Always lightly lubricate the O-ring with clean hydraulic fluid before assembly. Do not cross-thread the fitting — thread by hand until fully engaged before applying spanner. If the O-ring extrudes from the groove during assembly, stop, disassemble, and fit a new O-ring. A nicked O-ring will leak from first pressurisation. Frequently asked questions What is the difference between BSPP and BSPT? BSPP (British Standard Pipe Parallel, G-thread) has straight threads and seals using a bonded seal (Dowty washer) or O-ring pressed against a machined face — the threads themselves do not create the seal. BSPT (British Standard Pipe Tapered, R-thread) has a 1:16 taper that wedges into the port when tightened, sealing by thread interference plus thread sealant. Both have the same thread pitch and diameter for a given nominal size — the difference is whether the thread diameter is constant (parallel) or reduces toward the end (tapered). Measure with a calliper at two points to determine which you have. How do I identify what type of hydraulic fitting I have? Work through five steps: check the sealing method (flat face + O-ring = ORFS; 37° cone = JIC; O-ring at thread base = ORB; flat face, no O-ring = BSPP needs bonded seal; no visible sealing feature = tapered thread, BSPT or NPT); check parallel vs tapered with a calliper; measure thread OD; count threads per inch with a thread gauge; cross-reference against the BSP or JIC chart. If still uncertain, take the fitting to a hydraulic specialist — guessing on a hydraulic connection is not acceptable. What is a bonded seal and do I always need one with BSP fittings? A bonded seal (also called a Dowty washer or bonded seal washer) is a rubber-bonded metal washer that creates the hydraulic seal on BSPP (parallel BSP) connections. The seal sits between the machined face of the male fitting and the port face. Without it, a BSPP fitting cannot seal regardless of how tightly it is tightened — the parallel threads do not wedge together. You need one every time you assemble a BSPP connection. BSPT (tapered) connections do not use bonded seals. Always carry spare bonded seals in the sizes you work with. Can I use PTFE tape on hydraulic fittings? PTFE tape is only appropriate for tapered thread connections — BSPT or NPT — and even then, hydraulic-grade anaerobic thread sealant is generally preferred because it cures in the absence of air, fills the thread voids more reliably, and does not produce loose tape fragments that can contaminate the hydraulic system. Never use PTFE tape on BSPP (parallel BSP) ports — it prevents the bonded seal from seating correctly and will cause leaks. Never use PTFE tape on JIC, ORFS, or ORB fittings — those seals rely on metal contact or O-ring compression, not thread sealing. What is the difference between BSP and JIC fittings? BSP (BSPP) is a British Standard parallel thread that seals with a bonded seal at the port face. JIC is an American standard with a 37° cone nose that creates a metal-to-metal seal. They are completely incompatible — different thread form, different sealing method, different origin. BSP is common on older Australian and British-derived plant; JIC is common on American tractors and mobile equipment. The thread sizes are different (BSP uses its own pitch series; JIC uses UNF) so they will not physically mate in most cases, but always confirm with a gauge before assuming a fit is correct. What is ORFS and when should I use it? ORFS (O-ring face seal) is a flat-face fitting with an O-ring in a groove on the male face that seals when compressed against the matching flat female face. ORFS is specified on most new OEM hydraulic equipment worldwide because it offers superior leak resistance under vibration, tolerates over-torque better than JIC, and has a flat face design that resists contamination. If you are building new hydraulic circuits or replacing old JIC fittings on high-vibration applications, ORFS is the better specification. If the existing system is JIC and operating correctly, there is no need to convert. Are JIC and AN fittings interchangeable? Yes, for practical purposes. Both use a 37° cone seat on the same UNF thread sizes. AN fittings are manufactured to tighter aerospace tolerances and higher material grades, but the thread and cone geometry are identical. JIC and AN fittings of the same dash size will assemble and seal correctly together. In industrial and agricultural hydraulics, this distinction is not operationally significant. What is an ORB fitting? ORB (O-ring boss, SAE straight thread O-ring) is a fitting that threads directly into a port using UNF straight thread, with an O-ring at the base of the male thread that compresses against a chamfer at the port entrance. ORB is common on valve bodies, pump and motor ports, and manifolds on American-made hydraulic equipment. A key advantage is that adjustable-position ORB fittings can be backed off and repositioned for hose routing without breaking the seal. ORB and JIC use the same UNF thread sizes but seal entirely differently — do not interchange the male fittings between ORB ports and JIC swivel nuts. Can I connect BSP and NPT fittings together? No. BSP and NPT have the same taper rate (1:16) but different thread forms — BSP uses a 55° thread form, NPT uses 60°. In many common sizes they will physically thread together and may appear to hold briefly, but the mismatch in thread flank angles means the contact is not full and the connection will leak under pressure. This is one of the more dangerous fitting errors because the visual result looks correct. Always confirm thread type with a thread pitch gauge and use the correct dedicated adapters to convert between BSP and NPT. What hydraulic fittings are standard on Australian farm and construction equipment? It depends on the equipment origin. American-made tractors and construction equipment (John Deere, Case, New Holland, Caterpillar, Komatsu with American-spec components) predominantly use JIC on hose ends and ORB on port connections. British and older Commonwealth-origin equipment uses BSPP. European equipment (Deutz, Fendt, Liebherr, Volvo CE) uses DIN metric or ORFS. Most newer global-market equipment — regardless of brand — is moving toward ORFS for hose end connections. In practice, Australian workshops need to stock BSP, JIC, and ORFS as a minimum, with DIN metric for European machine coverage. What is the difference between reusable and crimped hydraulic fittings? Crimped fittings are permanently swaged onto the hose by a hydraulic crimping machine — they achieve rated hose pressure and are the production standard for most hydraulic hose assemblies. Reusable fittings use a threaded socket and insert assembly that grips the hose mechanically without a crimper, making them ideal for field repairs and remote locations. Reusable fittings have the same pressure rating as the hose when correctly matched and assembled. The limitations of reusable fittings are dependence on correct hose end preparation and the potential for incorrect assembly — always follow the manufacturer's fitting and hose combination specifications. Why is my hydraulic fitting leaking? The most common causes are: missing bonded seal on a BSPP connection; PTFE tape preventing the bonded seal from seating; wrong fitting type (e.g. JIC into ORFS port); damaged O-ring on an ORFS fitting; over-torqued and deformed JIC cone seat; cross-threaded NPT and BSPT fittings; under-torqued connection (JIC and ORFS both require correct torque to achieve full sealing force); or fitting damage from previous over-tightening. If a fitting leaks immediately after a new installation, the most likely causes are missing seal, wrong type, or damaged O-ring. If a previously sound connection starts leaking, vibration-induced loosening or O-ring/bonded seal degradation from heat or fluid incompatibility are the most common culprits. AIMS Industrial stocks hydraulic fittings across BSP, JIC, and ORFS standards, including stainless steel BSP fittings, reusable hose ends, bonded seals, and hydraulic adapters. If you need help identifying or matching a fitting, contact our team with the measurements from the 5-step guide above and we will help you source the right part. Share: Share on Facebook Share on X Pin on Pinterest Previous Post Pillow Block Bearings: Types, Selection & Installation Guide Next Post Wire Rope, Slings & Rigging Guide: WLL, Sling Angles & Shackles For butt weld fittings, see our butt weld fittings range stocked across Australia. AIMS Industrial stocks roll groove fittings — see the full range for trade and industrial use. 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