How to Identify a Hydraulic Fitting: Thread, Seat and Size
When you have a fitting in hand and no part number, identifying it comes down to four measurements. Get them right and you can match any fitting to a chart; guess and you order the wrong part or build in a leak. This guide walks through the exact steps so you can name any hydraulic fitting on your bench.
How do you identify an unknown hydraulic fitting?
The short answer: check four things in order, the sealing method (does it seal on the thread, a flared seat, or an O-ring), the thread angle (60 degrees for JIC, NPT, ORFS and SAE ORB; 55 degrees for BSP), the thread pitch or threads per inch, and the thread diameter. Those four data points identify almost any hydraulic fitting against a standard chart. Skip any one of them and visually similar fittings, like JIC 37 degree and SAE 45 degree flare, get mixed up.
Step 1: Is the thread tapered or parallel?
Tapered threads get narrower toward the end and seal by wedging metal on metal (NPT, BSPT). Parallel, or straight, threads stay the same diameter and seal on a seat or an O-ring, not on the thread (JIC, ORFS, BSPP, SAE ORB). Run a nut on by hand: if it spins freely down the whole thread it is parallel; if it tightens as it goes it is tapered.
Step 2: Measure the thread angle
Use a thread gauge. NPT, JIC, ORFS and SAE O-ring boss all use a 60 degree thread form; BSPP and BSPT use 55 degrees. This single check separates the American and British families before you go any further.
Step 3: Measure pitch and diameter
Measure crest-to-crest with a pitch gauge, or count the thread crests in a quarter inch and multiply by four for threads per inch. Then measure the thread diameter with calipers, the male outside diameter or the female inside diameter at the thread crests. Pitch plus diameter pin down the exact size.
Step 4: Confirm the seat or seal
This is where lookalikes separate. A cone seat measured at 37 degrees is JIC; 45 degrees is an SAE or automotive flare, and the two do not seal together. A flat face with an O-ring groove is ORFS. A straight thread with an O-ring at the base of the male is SAE O-ring boss (ORB). BSPP seals with a bonded washer or an O-ring under the hex, never on the thread.
Quick identification table
| Clue | Likely fitting |
|---|---|
| Tapered thread, 60 degrees | NPT / NPTF |
| Tapered thread, 55 degrees | BSPT |
| Parallel thread, 60 degrees, 37 degree cone seat | JIC 37 degree |
| Parallel thread, 60 degrees, flat face + O-ring | ORFS |
| Parallel thread, 60 degrees, O-ring at base of male | SAE ORB |
| Parallel thread, 55 degrees, bonded washer seal | BSPP |
Convert the size to a dash number and you have a complete, orderable spec.
Related range: Browse Velqor hydraulic fittings →
The goal is the right fitting first time, whether you buy from us or not
We wrote this so you can identify any fitting on your bench and order the exact match, wherever you source it. Four measurements, sealing method, thread angle, pitch and diameter, plus a chart, is all you need.
If you do want it sourced to spec, here is how we work: Velqor supplies hydraulic fittings and adapters matched to the thread standard, seat and size you specify, confirmed against your requirement and tested before dispatch. Send a photo with the four measurements, or a sample, and we will confirm the exact fitting rather than guess, and tell you plainly if a different connection would seal better.
Frequently Asked Questions
How do I tell JIC from an SAE 45 degree flare fitting?
They look almost identical, but the seat angle differs: JIC uses a 37 degree cone, SAE and automotive flare use 45 degrees. A seat-angle gauge tells them apart, and they must never be mated, because the mismatched seats will leak.
Do straight parallel threads seal on the thread?
No. Parallel threads such as JIC, ORFS, BSPP and SAE ORB seal on a flared seat, a flat-face O-ring, or an O-ring at the base of the thread. Only tapered threads (NPT, BSPT) seal on the thread itself.
How do I measure thread pitch without a gauge?
Count the thread crests in a quarter inch and multiply by four to get threads per inch, or measure the distance between two adjacent crests for metric pitch. An inexpensive thread pitch gauge is more reliable.
What is the difference between NPT and BSP?
Both come in tapered forms, but NPT uses a 60 degree thread form and BSP uses 55 degrees, so they do not seal together properly even at the same nominal size. Always confirm the thread angle before mating.
What four things identify any fitting?
Sealing method, thread angle, thread pitch (or TPI) and thread diameter. With those four you can match almost any hydraulic fitting to a standard identification chart.