Fitting Thread Identification Chart

What it is

Hydraulic fittings are identified by three things: the thread (form, pitch and whether it is tapered or parallel), the seat (flare angle, cone or flat face) and the sealing method (metal-to-metal, O-ring, bonded seal or thread interference). Fittings from different families can look alike and sometimes thread together part-way. They will not seal reliably. This chart lists the families most often seen in North American shops.

How to identify

1. Clean the fitting and look for an O-ring, a flat face or a cone.
2. Tapered or parallel? Lay a straightedge along the threads. Tapered threads (NPT, BSPT) narrow toward the end.
3. Measure the thread OD with calipers on the male, or the ID on the female.
4. Measure the pitch with a thread gauge (threads per inch or millimeters).
5. Check the seat angle with a seat angle gauge.
6. Match all three to the chart. One match is not enough.

Identification chart

Key points

• JIC and SAE 45° share several thread sizes. Only the seat angle tells them apart.
• ORB and JIC share thread sizes by dash number. ORB is a port; JIC is a flare.
• BSPP and NPT have similar pitches in some sizes (for example 1/2 and 3/4 at 14 TPI) but different thread angles. They do not seal together.
• Metric 24° fittings come in L and S series that share some threads with different tube sizes.

Common mistakes

• Identifying a fitting by thread size alone.
• Using thread sealant on fittings that seal on a flare, face or O-ring.
• Forcing a part-way thread engagement between two families.

Governing standards: SAE J514 (37° flare and ORB fittings); SAE J512 (45° flare); SAE J1453 (ORFS); SAE J1926 (straight thread ports); SAE J476 / ANSI B1.20.3 (Dryseal pipe threads); ISO 228-1 and ISO 7-1 (BSP threads); ISO 8434-1 (24° cone).

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.