American National Taper Pipe (N.P.T.)

Dash Size

 
Nominal
Thread
Size  - t.p.i.
 
Basic depth
of thread
(in.)
 
Outside dia.
of pipe (in.)
 
Effective
diameter
at small
end of
external
thread (in.) 
Basic
Minor
Dia. (in.)
 Recommended tap drill size (mm)
-1 1/16 - 27 .0296 .3125 .2712 .2812 6.30

-2

 1/8 - 27 .0296 .405 .3635 .3736 8.70
-4 1/4 - 18 .0444 .540 .4774 .4916 11.10
-6 3/8 - 18 .0444 .675 .6120 .6270 14.50
-8 1/2 - 14 .0571 .840 .7584 .7784 18.00
-12 3/4 - 14 .0571 1.050 .9677 .9889 23.25
-16 1 - 11-1/2 .0696 1.315 1.2136 1.2386 29.00
-20 1 1/4 - 11-1/2 .0696 1.660 1.5571 1.5834 38.00
-24 1 1/2 - 11-1/2 .0696 1.900 1.7961 1.8223 44.00
-32 2 - 11-1/2 .0696 2.375 2.2690 2.2963 56.00
-40 2 1/2 - 8 .1000 2.875 2.7195 2.7622 67.00 
American National Taper Pipe (N.P.T.)
Thread Form

h = Basic Depth of Thread = *8 p

p = Pitch = 1/t.p.i. (Threads per Inch)

Ref. Catalog Page 42 (Chart 3)

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