Pipe and gas threads often are available as parallel or tapered threads.

NPT taper of thread on diameter is 3/4 inch per foot.

BSP taper is 3/4 in per foor or 1 in 16 on the diameter or 1o 47'

NPT  

(American)

Thread angle 60o Taper 

NPSM National Standard free fitting Straight Mechanical Pipe Thread

  BSP  

(British)

Thread angle 55o Major Dia

Minor Dia

NPT size  (inch) TPI Basic Dia (male)

Basic Dia (male)

  BSP size  (inch) TPI Basic Dia (male)  
1/16 27 .312     1/16 28 0.304 0.2583
1/8 27 .405 0.390-0.397   1/18 28 0.383 0.3372
1/4 18 .540 0.517-0.526   1/4 19 0.518 0.4546
3/8 18 .675 0.653-0.662   3/8 19 0.656 0.5886
1/2 14 .840 0.813-0.823   1/2 14 0.825 0.7336
          5/8 14 0.902 0.8106
3/4 14 1.050 1.204-1.034   3/4 14 1.041 0.9496
          7/8 14 1.189 1.0976
1 11.5 1.315 1.281-1.293   1 11 1.309 1.1926
1 1/4 11.5 1.660 1.626-1.638   1 1/4 11 1.650  
1 1/2 11.5 1.900 1.865-1.877   1 1/2 11 1.882  
          1 3/4 11 2.116  
2 11.5 2.375 2.339-2.351   2 11 2.347 e&o.e.

 

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