NPT & NPSM Thread Identification Table

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NPT & NPSM Thread Identification

NPT – National Pipe Taper – ANSI/ASME B1.20.1-1983
NPSM – National Pipe Straight Mechanical – ANSI/ASME B1.20.1-1983

Dash
Size
Thread Size –
Threads Per
Inch
NPT Male
Thread Size
NPT Fixed Female
Thread Size
NPSM Female Swivel
Thread Size
usa Size – TPI mm Inch mm Inch mm Inch
-2 1/8 – 27 9.89 0.39 8.41 0.33 8.59 0.34
-4 1/4 – 18 13.19 0.52 11.21 0.44 11.89 0.47
-6 3/8 – 18 16.61 0.65 14.69 0.58 14.99 0.59
-8 1/2 – 14 20.61 0.81 17.79 0.71 19.09 0.75
-12 3/4 – 14 26.01 1.02 23.39 0.92 24.59 0.97
-16 1 – 11.5 32.49 1.28 29.49 1.16 30.49 1.2
-20 1.1/4 – 11.5 41.21 1.62 38.09 1.5 39.39 1.55
-24 1.1/2 – 11.5 47.31 1.85 43.89 1.73 45.51 1.79
-32 2 – 11.5 59.29 2.32 56.39 2.22 57.41 2.26

* Thread size refers to the nominal bore of the pipe.
Subtract approx. 1/4″ (6mm) from thread diameter measurement for nominal pipe size.

NPT & NPSM Thread Identification

 

NPT – NPT : NPT to fixed NPT female sealing is made through direct metal to metal contact. The use of Volz Thread Sealant is recommended.

 

NPT – NPSM : NPT male with conical 30° seat (60° included angle) seal against matching conical 30° seat of NPSM female swivel.