How to Identify an Unknown Hydraulic Fitting

Step 1: Visual Inspection

Before measuring anything, look at the fitting and answer these questions:

Is there an O-ring or O-ring groove? If yes, it is likely ORB, ORFS, or possibly a metric flat-face fitting.

Is there a cone seat (angled surface inside the nut)? If yes, it is likely JIC (37-degree) or DIN (24-degree). JIC cones appear visually steeper than DIN.

Is there a flat face on the fitting end? If yes, it is likely ORFS or BSPP with a bonded washer.

Are the threads visibly tapered? If yes, it is NPT or BSPT.

Does the fitting have a cutting ring (a small metal ring around the tube)? If yes, it is DIN metric compression.

Step 2: Thread Type

Use a thread pitch gauge to determine the thread pitch. Then measure the outside diameter with a caliper.

If the pitch is in TPI (threads per inch): The fitting is from the SAE/imperial family: JIC, NPT, ORB, or ORFS.

If the pitch is in mm: The fitting is metric: DIN, or possibly metric BSP.

If the thread angle is 55 degrees (Whitworth): The fitting is BSP (either BSPT tapered or BSPP parallel).

Step 3: Elimination by Seal Type

Once you know the thread family, the seal type narrows the identification:

Imperial threads + taper: NPT Imperial threads + straight + O-ring on boss: SAE ORB Imperial threads + straight + flat face with O-ring: ORFS Imperial threads + straight + 37-degree flare cone: JIC Whitworth threads + taper: BSPT Whitworth threads + straight + flat face: BSPP Metric threads + 24-degree cone: DIN compression Metric threads + flat face with O-ring: Metric ORFS equivalent

Common Confusion Points

JIC vs ORB: Both use straight UNF threads. JIC has a 37-degree cone seat. ORB has an O-ring groove. If you see an O-ring groove on the male fitting body, it is ORB. If you see a flare cone inside the swivel nut, it is JIC.

NPT vs BSPT: Both are tapered. NPT has a 60-degree thread angle. BSPT has a 55-degree angle. A thread gauge designed for one will not seat perfectly in the other. NPT seals on thread deformation. BSPT often uses a bonded washer or sealant.

ORB vs ORFS: Both have O-rings. ORB seats the O-ring against a boss face (the machined flat surface around the port). ORFS seats the O-ring between two flat mating faces. ORB O-rings are on the male fitting body. ORFS O-rings are on the flat face of the fitting.

When in Doubt

If you cannot identify the fitting with certainty, take it to a hydraulic supply house. They have identification kits with thread gauges, go/no-go gauges, and sample fittings for every standard. Guessing and forcing the wrong fitting into a port damages threads and creates a leak that may not appear until the system is under pressure.

Never mix standards. A JIC fitting threaded into an ORB port may engage the threads but the seal will not function correctly. The result is a connection that feels tight but leaks under pressure.