Hydraulic hoses and fittings
Hydraulic fittings and hoses are the most common connection components in fluid power systems, with working pressures typically exceeding 690 bar / 10 000 psi in high-demand applications. Standardized fittings SAE J514 (JIC 37°), SAE J1453 (ORFS) and BSPP threads (ISO 228) enable leak-tight connections via conical surfaces, flat seats with O-ring, or integrated elastomeric seals. Correct sizing of hose and fitting relies on the “dash size” nomenclature and unified thread pitch standards (UNC/UNF) or metric.
Types and standards
Section titled “Types and standards”JIC Fittings (SAE J514)
Section titled “JIC Fittings (SAE J514)”With a 37° flared seat, these fittings ensure metal‑to‑metal sealing up to 690 bar / 10 000 psi. They are dimensionally equivalent to AN (Army‑Navy) fittings but with less restrictive industrial tolerances. The 37° angle is not interchangeable with the 45° SAE flare (SAE J512), although dash sizes 2, 3, 4, 5, 8 and 10 share the same thread pitch. Threads are UNF per ANSI B1.1 and sealing occurs between the connector nose and the inside of the flared tube, with a sleeve that distributes the nut compression.
ORFS Fittings (SAE J1453)
Section titled “ORFS Fittings (SAE J1453)”ORFS (O‑Ring Face Seal) fittings incorporate an O‑ring in the face of the flat seat, which eliminates the risk of vibration‑induced leaks and facilitates assembly without critical tightening torque. They are used in circuits where reliable sealing is a priority, even at pressures above 420 bar / 6000 psi.
BSPP Fittings (ISO 228‑1)
Section titled “BSPP Fittings (ISO 228‑1)”BSPP parallel thread uses an inverted conical seat or an O‑ring in the male fitting housing. Although its use is common in Europe, compatibility with NPT or metric threads requires specific adapters. Maximum service pressures reach 250 bar / 3625 psi in small sizes and decrease in larger diameters.
Technical specifications
Section titled “Technical specifications”Hydraulic fitting selection is based on the combination of thread (UNC, UNF, BSPP, metric ISO), seat type (37° or 45° flare, flat face with O‑ring), and material (forged carbon steel, stainless steel, brass, Monel). The following table lists the critical dimensions of JIC fittings per SAE J514.
| Designation (dash) | UNF Thread | Tube Outer Diameter (mm / in) | Fitting Inner Diameter (mm / in) | Fitting Total Length (mm / in) |
|---|---|---|---|---|
| 2 | 5/16‑24 UNF | 3,18 mm / 0,125 in | 1,57 mm / 0,062 in | 11,38 mm / 0,448 in |
| 3 | 3/8‑24 UNF | 4,76 mm / 0,188 in | 3,18 mm / 0,125 in | 12,16 mm / 0,479 in |
| 4 | 7/16‑20 UNF | 6,35 mm / 0,250 in | 4,37 mm / 0,172 in | 13,97 mm / 0,550 in |
| 5 | 1/2‑20 UNF | 7,94 mm / 0,313 in | 5,94 mm / 0,234 in | 13,97 mm / 0,550 in |
| 6 | 9/16‑18 UNF | 9,53 mm / 0,375 in | 7,14 mm / 0,281 in | 14,12 mm / 0,556 in |
| 8 | 3/4‑16 UNF | 12,70 mm / 0,500 in | 10,31 mm / 0,406 in | 16,69 mm / 0,657 in |
| 10 | 7/8‑14 UNF | 15,88 mm / 0,625 in | 13,49 mm / 0,531 in | 19,25 mm / 0,758 in |
| 12 | 1 1/16‑12 UN | 19,05 mm / 0,750 in | 15,47 mm / 0,609 in | 23,95 mm / 0,943 in |
UNF Thread Dimensions Table for JIC Fittings
Section titled “UNF Thread Dimensions Table for JIC Fittings”Unified Fine Thread (UNF) is the standard for most JIC and ORFS connections. Its pitches are specified in threads per inch and correspond to Class 2 fit for general applications. The following table shows the dimensional values of the most commonly used threads in hydraulics.
| Thread Designation | Threads per Inch | Major Diameter (mm / in) | Pitch (mm / in) |
|---|---|---|---|
| 5/16‑24 UNF | 24 | 7,94 mm / 0,313 in | 1,058 mm / 0,0417 in |
| 3/8‑24 UNF | 24 | 9,53 mm / 0,375 in | 1,058 mm / 0,0417 in |
| 7/16‑20 UNF | 20 | 11,11 mm / 0,438 in | 1,270 mm / 0,0500 in |
| 1/2‑20 UNF | 20 | 12,70 mm / 0,500 in | 1,270 mm / 0,0500 in |
| 9/16‑18 UNF | 18 | 14,29 mm / 0,563 in | 1,411 mm / 0,0556 in |
| 3/4‑16 UNF | 16 | 19,05 mm / 0,750 in | 1,587 mm / 0,0625 in |
| 7/8‑14 UNF | 14 | 22,23 mm / 0,875 in | 1,814 mm / 0,0714 in |
| 1 1/16‑12 UN | 12 | 26,99 mm / 1,063 in | 2,117 mm / 0,0833 in |
Materials and Applications
Section titled “Materials and Applications”Hydraulic fittings are manufactured in forged carbon steel (galvanized or dichromated) for most fluid power systems, 316 stainless steel for corrosive environments or food/pharmaceutical sectors, and copper‑nickel alloys (Monel) or brass in marine and instrumentation applications. Thermoplastic hoses with one or two steel braid reinforcements withstand pressures up to 280 bar / 4000 psi, while wire spiral (4 and 6 layers) reach 450 bar / 6500 psi. Compatibility of the inner elastomer (NBR, EPDM, HNBR, FKM) with the hydraulic fluid is decisive for the assembly’s service life.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the difference between a JIC fitting and a SAE 45° fitting?
Section titled “What is the difference between a JIC fitting and a SAE 45° fitting?”JIC fittings have a 37° flared seat while SAE (J512) use 45°; they are not interchangeable despite sharing threads on dash sizes 2, 3, 4, 5, 8 and 10. The maximum working pressure of a JIC is 690 bar / 10 000 psi, compared to the typical 210 bar / 3000 psi of SAE 45° in hydraulic systems.
What is the service pressure of an ORFS fitting?
Section titled “What is the service pressure of an ORFS fitting?”A standard ORFS fitting achieves working pressures of 420 bar / 6000 psi in small diameters, dropping to 280 bar / 4000 psi for dash 16 (-16). Sealing with a Viton® O‑ring allows temperatures from –40 °C to +120 °C / –40 °F to +248 °F.
How are BSPP and metric hydraulic threads identified?
Section titled “How are BSPP and metric hydraulic threads identified?”BSPP (parallel) thread is measured with a thread gauge and verified with BSPP thread pitch gauges; typical outer diameters are 25.4 mm / 1 inch for G1, 19.05 mm / 0.75 in for G3/4. Metric threads per DIN 7631 have a fine pitch of 1.5 mm / 0.059 in for M22x1.5, while JIC adapters use UNF with pitch in threads per inch.
What tightening torque does a 3/4″ (-12) JIC fitting require?
Section titled “What tightening torque does a 3/4″ (-12) JIC fitting require?”For a JIC connection of dash 12 (1 1/16‑12 UN) a tightening torque of 115‑125 Nm / 85‑92 lb‑ft is recommended. Excessive tightening can damage the flare and reduce service life to less than 1000 pressure cycles.
What hose size corresponds to a -8 JIC fitting?
Section titled “What hose size corresponds to a -8 JIC fitting?”The -8 (dash 8) designation corresponds to a tube outer diameter of 12.70 mm / 0.50 inches and the standard hydraulic hose with double braid reinforcement has an inner diameter of 12.5 mm / 1/2 in, suitable for flow rates up to 100 L/min / 26.4 gpm in return.
Can a JIC fitting be combined with a Komatsu or JIS flare?
Section titled “Can a JIC fitting be combined with a Komatsu or JIS flare?”Not directly. Komatsu and JIS flares use 30° and metric threads (Komatsu) or BSP (JIS), while JIC uses 37° and UNF threads. A 30° to 37° adapter is required that maintains the sealing class up to 250 bar / 3625 psi.
References
Section titled “References”- engineeringtoolbox.com: https://www.engineeringtoolbox.com/unified-screw-threads-unc-unf-d_1809.html
- engineersedge.com: https://www.engineersedge.com/iso_hardware_menu.shtml
- efunda.com: https://www.efunda.com/designstandards/oring/oring_as568.cfm