NPT NPTF (Dryseal) NPS (Straight) NPSF (Dryseal)
Designation Pipe size O.D. TPI Tap drill size Decimal tap drill size Tap drill size Decimal tap drill size Tap drill size Decimal tap drill size Tap drill size Decimal tap drill size
1/16 - 27 .3125 27 D 0.2460 D 0.2460 1/4 0.2500 1/4 0.250
1/8 - 27 405 27 Q 0.3320 R 0.3390 11/32 0.3438 Q 0.332
1/4 - 18 .540 18 7/16 0.4375 7/16 0.4375 7/16 0.4375 7/16 0.438
3/8 - 18 .675 18 9/16 0.5625 37/64 0.5781 37/64 0.5781 37/64 0.578
1/2 - 14 .840 14 45/64 0.7031 45/64 0.7031 23/32 0.7188 45/64 0.703
3/4 - 14 1.05 14 29/32 0.7813 59/64 0.9219 59/64 0.9219 59/64 0.922
1 - 11 1/2 1.315 11.5 1 9/64 1.1406 1 5/32 1.1563 1 5/32 1.1563 1 5/32 1.156
1 1/4 - 11 1/2 1.660 11.5 1 31/64 1.4844 1 1/2 1.5000 1 33/64 1.5156
1 1/2 - 11 1/2 1.9 11.5 1 47/64 1.7344 1 47/64 1.7344 1 3/4 1.7500
2 - 11 1/2 2.375 11.5 2 13/64 1.2031 2 7/32 2.2188 2 7/32 2.2188
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Last Updated: 20 February 2015