Hydraulic thread chart. Every common port and connector, by dash size.

NPT and NPTF taper, and seal on the thread itself — NPTF by crushing the crests, NPT with sealant. NPSM is straight and seals on a 30° seat inside the female swivel, which also mates a chamfered NPTF male.

All three share a pitch at every size, so a pitch gauge alone cannot separate them. Hold a straight edge along the male: a taper shows daylight at one end.

Same UN/UNF thread, three different seals. JIC seals metal to metal on a 37° flare. ORB seals with an O-ring pressed into a chamfer at the port face. Flareless seals where a sleeve bites into the tube on a 24° seat.

Because the thread is identical, measuring it only narrows the field to these three. Look at the end: a cone is JIC, an O-ring under a flat face is ORB, a sleeve on a tube is flareless.

An O-ring in a groove on the male face is squeezed flat against the female’s machined face. The thread only clamps.

ORFS threads are a size larger than JIC at the same dash: a -6 ORFS is 11/16-16, a -6 JIC is 9/16-18.

Metal to metal on a 45° flare. Low-pressure duty: fuel, refrigerant and instrument air.

Up to -10 the threads match JIC except at -6 (5/8-18 here, 9/16-18 on JIC). The seat angle is what separates them, and a 37° and a 45° seat never seal on each other.

The male tube nut clamps a double-flared 45° tube end onto a 42° seat inside the female fitting. Brake and fuel lines on vehicles.

An O-ring in the flange head seals on the flat port face; two clamp halves and four bolts hold it.

There is no thread to measure. Measure the bolt spacing on the long side: at every size Code 62 is wider and its head is thicker, and the two codes never interchange.

BSPP is parallel and seals with a bonded washer, an O-ring or a 60° cone in the female swivel. BSPT tapers and seals on the thread. JIS 30° flare uses the BSPP thread with a 30° seat.

The 55° flank angle and these pitches separate BSP from NPT: at 1/2" both are 14 TPI, but a BSP male measures 20.96 mm against NPT’s 21.34 mm.

ISO 6149 ports seal with an O-ring in a chamfer, like SAE ORB, and carry a ring groove on the spot face to say so. ISO 9974 and DIN 3852 ports seal on a flat face with a bonded washer or edge seal.

A metric thread is named by its real size: M18×1.5 is 18 mm across the crests with 1.5 mm between them. The female figure is the tap drill size.

A cutting ring bites into plain metric tube as the nut is made up on a 24° cone.

The same thread can be two different fittings: M22×1.5 is a 15 mm light-series fitting and a 14 mm heavy-series one. Name the tube O.D. and the series, never the thread alone.

Metric parallel thread with a 30° seat. Found across Komatsu machines and some other Japanese equipment.

Easily mistaken for metric 24° cone fittings of the same thread. The seat angle settles it.