JIC Thread Pitch Chart: TPI, mm Pitch and Thread ID

JIC threads are UNF up to -10 and 12-pitch UN from -12 up. Here is the TPI and mm pitch of every size, and a table to identify a thread by OD and pitch.

Last updated October 30, 2026. Reference values; verify against manufacturer specifications.

Every JIC fitting uses a 60° inch thread with a fixed pitch for each size. From -2 to -10 the threads are UNF (fine); from -12 upward they are 12-pitch UN, so all the large sizes have 12 threads per inch. This page lists the pitch of every JIC size in TPI and millimetres, shows which sizes share a pitch, and gives an identification table that sorts JIC and its look-alikes by measured diameter.

JIC thread pitch chart

Threads per SAE J514 as published by Parker and Eaton. Pitch in mm is 25.4 ÷ TPI. ORB ports use the same thread as the JIC tube end of the same dash (SAE J1926); SAE 45° and ORFS shares per the Eaton and Parker identification guides.

What UNF and UN mean on a JIC thread

UNF is the Unified National Fine series, and UN with a pitch number (12-UN) is a constant-pitch Unified thread. Both have the same 60° thread form; the only difference is how the pitch is chosen. Fine-series pitches get coarser as the diameter grows, which is why the small JIC sizes step from 24 to 20, 18, 16 and 14 TPI. From -12 up, SAE J514 holds the pitch at 12 TPI for every size.

JIC threads are made to the standard commercial thread class, 2A for male and 2B for female threads. AN fittings use the same sizes with the tighter 3A/3B class; see JIC vs AN.

JIC sizes grouped by pitch

A thread gauge narrows a fitting down to one pitch group. Within a group, the caliper reading decides the size:

The 12 TPI group is where most mistakes happen with large fittings. A -12, -14 and -16 all accept the same gauge leaf, and their diameters differ by only about 3.2 mm per step. Measure the diameter to at least a tenth of a millimetre.

Inch pitch vs metric pitch

None of the JIC pitches is a standard metric pitch, but some come close over a few threads:

• 18 TPI = 1.411 mm, close to a 1.5 mm metric pitch. A -6 JIC and an M14x1.5 thread differ by only about 0.3 mm in diameter.
• 16 TPI = 1.588 mm, also close to 1.5 mm. Over ten threads the difference is less than 1 mm.
• 12 TPI = 2.117 mm, close to a 2 mm metric pitch.

Check the pitch over as many threads as the gauge covers. If an inch leaf rocks slightly and a metric leaf sits flush, the fitting is not JIC. The JIC metric conversion chart has the metric threads most often mixed up with JIC.

Thread identification by measured OD and pitch

This table lists the male thread diameter of JIC and the fittings most often confused with it, sorted from smallest to largest. Find your caliper reading, then use the pitch and the seat to pick the right row. Real threads usually measure a few tenths of a millimetre under the nominal size.

JIC, SAE 45° and ORFS values are nominal major diameters (SAE J514, J512, J1453 as published by Eaton and Parker). NPT values are approximate measured diameters from the Eaton and McGill guides, which vary along the taper. BSP values are major diameters from ISO 228-1. Metric values are nominal. Fittings that share a JIC thread exactly are listed in the JIC row rather than as separate rows.

How to read a thread with a gauge

1. Clean the thread with a brush so dirt does not hold the gauge off the crests.
2. Press the gauge leaf into the thread along the axis of the fitting, not at an angle.
3. Hold it up to a light. A correct leaf shows no light between the teeth and the thread along its whole length.
4. Try the leaves on either side to confirm. If two leaves both look close, count threads over a measured inch instead.
5. Check the thread angle: a 55° Whitworth leaf on a BSP thread fits better than a 60° leaf.

More on tools and readings: how to measure JIC fittings, and the interactive finder on the JIC identification page.

References

SAE J514 threads as published by Parker and Eaton; Maxbar JIC J514 end-fitting chart (thread class); Eaton Thread Identification Guide; McGill Hose thread identification guide; ISO 228-1 (BSP major diameters). Values are reference only.

Frequently asked questions

What is the thread pitch of a JIC fitting?

It depends on size: 24 TPI for -2 and -3, 20 for -4 and -5, 18 for -6, 16 for -8, 14 for -10, and 12 TPI for -12 and every larger size.

Are JIC threads UNF?

From -2 to -10, yes. From -12 upward they are 12-pitch UN threads, which have the same 60° form with a constant 12 TPI.

What is 18 TPI in mm?

1.411 mm per thread (25.4 ÷ 18). It is close to, but not the same as, a 1.5 mm metric pitch.

How do I tell a -12 from a -16 JIC if both are 12 TPI?

Measure the diameter. A -12 male is about 1.06 in (27.0 mm), a -14 about 1.19 in (30.2 mm) and a -16 about 1.31 in (33.3 mm).

Do JIC and ORB use the same thread pitch?

Yes. An SAE O-ring boss port uses the same thread as the JIC tube end of the same dash number. They seal differently, so they are not interchangeable.