NPT American Taper Pipe Thread
ANSI B 1.20.1

American Taper Pipe Thread, with sealant compound. National Pipe Taper (1:16)
The flank angle is 60°, the profile was originated by William Sellers.

Nominal Diameter Major Diameter
mm
Tapping
Drill Size
mm
TPI Pitch
mm
1/16" - 27 NPT 7.895 6.00 27 0.941
1/8" - 27 NPT 10.242 8.25 27 0.941
1/4" - 18 NPT 13.616 10.70 18 1.411
3/8" - 18 NPT 17.055 14.10 18 1.411
1/2" - 14 NPT 21.223 17.40 14 1.814
3/4" - 14 NPT 26.568 22.60 14 1.814
1" - 11 1/2 NPT 33.228 28.50 11.5 2.209
1 1/4" - 11 1/2 NPT 41.985 37.00 11.5 2.209
1 1/2" - 11 1/2 NPT 48.054 43.50 11.5 2.209
2" - 11 1/2 NPT 60.092 55.00 11.5 2.209
2 1/2" - 8 NPT 72.699 65.50 8 3.175
3" - 8 NPT 88.608 81.50 8 3.175
3 1/2" - 8 NPT 101.316 94.30 8 3.175
4" - 8 NPT 113.973 107.00 8 3.175
5" - 8 NPT 141.300 134.384 8 3.175
6" - 8 NPT 168.275 161.191 8 3.175
8" - 8 NPT 219.075 211.673 8 3.175
10" - 8 NPT 273.050 265.311 8 3.175
12" - 8 NPT 323.850 315.793 8 3.175