The kit
What each tool tells you
No single reading names a thread. Diameter narrows the field, pitch separates the families, and the seat angle breaks the ties between look-alikes.
Thread diameter — the size group
Pitch — TPI or millimetres
Sealing angle — the tiebreaker
Step 01 — Before you measure
Read how it seals first
A quick look points you to the right family before a tool comes out — exactly how the bench works it. Two things to settle:
- Parallel or tapered? Tapered threads close in toward the tip and seal on the threads themselves (pipe threads like NPT and BSPT). Parallel threads stay even and seal on a cone, face or O-ring.
- How does it seal? A cone seat, a flat face with an O-ring, an O-ring at the base, or a soft washer. The seal style alone rules several standards in or out.
Step 02 — Tool 1
The caliper — thread diameter
Measure across the thread at its widest point, at the first full thread near the end of the fitting. Keep the caliper jaws square to the thread so you catch the true diameter.
- Male threads point outward — measure the outside diameter (OD) across the crests.
- Female threads point inward — measure the inside diameter (ID) across the bore.
- Read in both inches and millimetres if you can; the tables list both, and metric vs. inch is itself a clue.
Step 03 — Tool 2
The pitch gauge — threads per inch or millimetres
Lay each leaf of the gauge across the threads and hold the pair up to a light. When a leaf seats with no light showing between its teeth and the thread, that leaf is your pitch.
- Imperial gauge reads threads per inch (TPI) — e.g.
14,18,20. - Metric gauge reads pitch in millimetres — e.g.
1.5,2.0. - No gauge handy? Count the threads in a quarter-inch and multiply by four, or measure crest-to-crest.
Step 04 — Tool 3
The seat-angle gauge — the tiebreaker
When the diameter and pitch match but two standards still look the same, the sealing surface decides it. A seat-angle gauge sits in the cone and reads the half-angle.
- 24° metric DIN · 30° JIS and BSPP cone · 37° JIC · 45° SAE flare.
- No cone? The seal is a flat face with an O-ring (ORFS) or an O-ring at the base (SAE ORB).
- Watch for dual seats — a fitting can carry both 37° and 45° — and rounded "radiused" cones.
Step 05 — Put it together
A worked example
Say you're holding a male fitting off a tractor and you want a name for it.
Three readings, one answer
- Caliper across the crests:
0.75"(19.05 mm) OD. - Pitch gauge meshes clean on the
16 TPIleaf. - Threads are parallel, the seal is metal-to-metal on a cone.
So far that points at a 3/4"-16 straight thread with a cone seat — which is a dash-8 in both JIC and SAE 45°. They share the identical thread, so diameter and pitch can't separate them. The seat gauge does:
Seat reads 37° → it's a JIC 37° -8. (Reads 45° → it's an SAE -8.)
From here, take the readings to the matching row in the thread size tables to confirm, then mate a known fitting as the final check.
| Reading | What it rules in or out |
|---|---|
| Parallel / tapered | Tapered points to pipe threads (NPT, BSPT). Parallel points to cone, face or O-ring seals. |
| Diameter | Narrows to a size group, but rarely names the standard on its own. |
| Pitch | Separates families of similar size — for example 55° BSP from 60° NPT. |
| Seat angle | The tiebreaker between look-alikes: JIC 37° vs SAE 45°, DIN 24° vs JIS 30°. |
| Seal type | Cone, flat O-ring face, O-ring boss or washer — settles ORFS vs JIC vs ORB. |
Measured it and still not sure?
Send us your three readings — or just a photo — and we'll name the thread and pull the right adapter from any of our Edmonton, Calgary or Acheson branches.