The Catalogue

Threads

The non-standardisation of thread types and fittings used on cars, bikes, boats, etc can make life difficult when it comes to modifying them for competition use. (Purpose-built racers are usually a little better, but not always). The information given below will help to identify most thread sizes and types found in common usage. Uncommon and antique threadforms may be difficult to identify, but if you have any queries EXACT`s Technical Department will be happy to provide advice and assistance.

JIC / SAE 37 degree / UNF Straight.

These three threadforms share the same dimensions and thread pitches in all sizes. The only effective difference is that JIC (also known as SAE 37 degree) has a conical seating face (37 degree or 74 degree total angle) and UNF Straight has a flat seat - sealing being effected by use of a washer. Male JIC fittings have a convex cone, female fittings a concave cone. JIC (also called AN from its American Army/Navy usage) is the most widely-used thread type in competition or high performance plumbing. Most hose ends are made to this specification. (There is, also, an SAE 45 degree threadform which has a 45 degree conical seat. It shares the same dimensions as JIC exept for the angle of its seat and in its 1"1/16 size when it has 14t.p.i.. It is rare outside refrigeration and air conditioning plant and its use should be avoided as any seal it may produce with a JIC fitting cannot be guaranteed).

   

The AN dash sizes were originally used for hard metal tubing - the dash number indicated the outside diameter in increments of 1/16". From this the inside diameter could be calculated (as the piping used was standardised). This convention was carried over to flexible hoses - the dash size being used to indicate the internal diameter of the hose (in 1/16"). This is no longer the case - if you need to know the internal diameter of EXACT hose, consult the Hose Data given in the 300 Series Hose section.

JIC Thread Dash Size Thread Size Male Thread O.D. (ins) Female Thread I.D. (ins)
-02 5/16x24 0.3125 0.2614
-03 3/8x24 0.3750 0.3299
-04 7/16x20 0.4375 0.3762
-05 1/2x20 0.5000 0.4387
-06 9/16x18 0.5625 0.4943
-08 3/4x16 0.7500 0.6733
-10 7/8x14 0.8750 0.7874
-12 1"1/16x12 1.0625 0.9603
-16 1"5/16x12 1.3125 1.2103
-20 1"5/8x12 1.6250 1.5140
-24 1"7/8x12 1.8750 1.7728
-28 2"1/4x12 2.2500 2.1478
-32 2"1/2x12 2.5000 2.3978

B.S.P.

British Standard Pipe thread was widely used on British cars and components and is still found in use today. Male fittings have a 60 degree concave cone seating, females a convex cone (the opposite of JIC). There is also a tapered form - B.S.P.T. - but this is little used in competition plumbing, although it is found on older British cars. B.S.P. fittings occasionally use a Dowty washer (or similar) under their hex to effect a seal. (Female fittings will sometimes have a globeseal seat instead of a cone). B.S.P. is also found on the Japanese motor industry's past history as a producer of British cars (J.I.S.). There is also an inverted version of J.I.S. where the male fitting has a convex seat, the female a concave.

Beware of anything made in the USA. If you think it looks like a BSP taper thread, it is probably not. The americans do not recognize BSP. It will be more likely to be a NPT taper thread. The difference between them in the smaller sizes is only one TPI (threads per inch). So they will fit each other briefly before trying to wreck it !

Nominal Thread Size Male Thread O.D. (ins) Female Thread I.D. (ins)
1/8x28 0.383 0.337
1/4x19 0.518 0.451
3/8x19 0.656 0.589
1/2x14 0.825 0.734
5/8x14 0.902 0.811
3/4x14 1.041 0.950

N.P.T.F.

National Pipe Tapered Fuel is an American tapered thread widely used today by American manufacturers. As with B.S.P.T., the seal is made by deformation of the threads. In both cases the use of P.T.F.E. sealant tape (or similar) should be used to assist sealing.

Thread Male Thread O.D. (ins) Female Thread I.D. (ins)
1/8x27 0.4063 0.3438
1/4x18 0.5625 0.4688
3/8x18 0.6875 0.5938
1/2x14 0.8438 0.7188
3/4x14 1.0625 0.9375
1"x11 1/2 1.3125 1.1875

DIN 7631 / 7647 & DIN3901 / 3902

These are German specifications which are identical in threadform exept in their 30mm sizes - 7631/2 has 30x1.50 pitch, 3901/2 has a 30x2.00 pitch. DIN 7631/2 has a 60 degree conical seat, 3901/2 has a 20 degree cone. DIN 3901/2 is easy to identify as its sealing is achieved by use of a compression olive.

Thread Size Male Thread O.D. (mm) Female Thread I.D. (mm)
10x1.00 10 8.5
12x1.50 12 10.5
14x1.50 14 12.5
16x1.50 16 14.5
18x1.50 18 16.5
22x1.50 22 20.5
26x1.50 26 24.5
30x1.50 30 28.5

S.A.E. Inverted

Similar to but not the same as JIC. Some sizes are the same pitch, but the angle of the seating cone is different (sometimes 42 degrees, sometimes 45 degrees). Automotive engineering has a lot to answer for! This thread will most commonly be encountered on power steering systems (and occasionally on fuel lines) where it will appear as a tube nut on a flared pipe (as in brake pipes).

Thread Size Male Thread O.D. (ins) Female Thread I.D. (ins)
5/16x28 0.3125 0.2813
3/8x24 0.3750 0.3438
7/16x24 0.4375 0.4063
1/2x20 0.5000 0.4375
5/8x18 0.6250 0.5625
11/16x18 0.6875 0.6250
3/4x18 0.7500 0.6875
7/8x18 0.8750 0.8125
1"1/16x16 1.0625 1.0000