NPT Threads Information Sheet

NPT stands for National Pipe Thread and is an American standard thread type.

It is also referred to as MPT , MNPT or NPT (M) for male outside threads and FPT, FNPT or NPT(F) for female inside  threads.

A thread sealant is advisable to achieve a leak free seal.  

Please keep in mind that "NPT" is a nominal Industrial nomenclature size rather than actual diameter.

The table below gives the Threads Per Inch and Actual Diameter for NPT Threads in US Inches.

1/8 NPT: Theads Per inch: 27,  Actual Thread Diameter 0.405"

1/4 NPT: Threads Per Inch: 18, Actual Thread Diameter 0.540"

3/8 NPT: Threads Per Inch: 18, Actual Thread Diameter 0.675"

1/2 NPT: Threads Per Inch: 14, Actural Thread Diameter 0.840"

1 NPT: Threads Per Inch: 11-1/2, Actual Thread Diameter 1.050"

1-1/4 NPT: Threads Per Inch: 11-1/2, Actual Thread Diameter 1.660"

1-1/2 NPT: Threads Per Inch: 11-1/2, Actual Thread Diameter 1.900"

2 NPT: Threads Per Inch: 11-1/2, Actual Thread Diameter 2.375"

2-1/2 NPT: Threads Per Inch: 8, Actual Thread Diameter 2.875"

3 NPT: Threads Per Inch: 8, Actual Thread Diameter 3.50"

4 NPT: Threads Per Inch: 8, Actual Thread Diameter 4.50"

Please note that NPT fittings should be hand tightend and then another 2 to 4 turns and no more.  More turns will but too much pressure on the fitting and may crack it and cause a leak.  The smaller the NPT size the easier it is to crack. 

Copyright © 2018 Coyote Gear