HELIVIQ Team · Published 18 October 2026
A hydraulic fitting that almost fits is the most expensive kind. It cross-threads, leaks at pressure or seals only until the first pressure spike. Identifying the thread properly takes a caliper, a thread gauge and two minutes.
Step 1: measure the outside diameter
Measure across the crests of a male thread with a vernier caliper. For a female thread, measure the inside diameter at the crests; it will be slightly smaller than the male thread it accepts. Measure on an undamaged section.
Step 2: measure the pitch
Use a thread pitch gauge. Inch threads are counted in threads per inch; metric threads are measured as the distance between crests in millimetres. Try both leaf sets until one sits in the thread with no light showing.
Step 3: check the seal
- A 37° cone seat points to JIC
- A flat face with an O-ring groove points to ORFS
- A 24° cone with a cutting ring or O-ring points to metric DIN
- A bonded washer, O-ring or 30° cone on a parallel thread points to BSPP
- A thread that narrows along its length and seals on the thread itself points to NPT
Step 4: compare with the standard table
With diameter, pitch and seal type, the standard is usually clear. Some sizes are close — a 1/4 BSP and a 1/4 NPT differ by about half a millimetre — so check for taper before deciding.
Our free thread identifier does this comparison for you and lists the closest BSP, NPT, JIC, ORFS and metric matches, with hose dash sizes. If the thread is worn or unusual, send a photo with a ruler on WhatsApp and we will confirm it before you order.