Identifying Hydraulic Thread Types

What it is

Many thread types look alike. Two fittings can share a thread but seal differently, or seal the same way with different threads. Identification uses three facts:

• How it seals: metal-to-metal cone or flare, O-ring, or taper thread.
• Thread: outside diameter and pitch, inch or metric, straight or tapered.
• Seat angle: the angle of the flare or cone where sealing happens.

How to identify

1. Clean the fitting. Dirt and paint hide threads and seats.
2. Look for an O-ring. An O-ring on a flat face means ORFS. An O-ring at the base of a straight thread means an O-ring boss (ORB) or metric port.
3. Check for taper. Tapered threads (NPT, NPTF, BSPT) get smaller toward the end.
4. Measure the thread OD with a caliper. Measure the inside diameter of female threads.
5. Measure the pitch with a thread pitch gauge (threads per inch or millimeters).
6. Measure the seat angle with a seat angle gauge.
7. Compare against a chart. See Hydraulic Thread Identification Chart.

Common types

Key points

• JIC 37° and SAE 45° can share the same thread size but will not seal together.
• NPT and BSPT look alike; the thread forms differ (60° vs 55°).
• Metric fittings often need both pitch and cone checks.
• Use a pitch gauge before a caliper. The pitch narrows the family quickly.

Common mistakes

• Identifying by thread alone without checking the seat or seal.
• Forcing a fitting that "almost" fits.
• Measuring worn threads on the male side only.
• Mixing JIC and 45° flare parts.

Governing standards: SAE J514 (hydraulic tube fittings); SAE J1926 (straight-thread O-ring ports); SAE J1453 (O-ring face seal fittings).

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.