Unified Thread Series 20 TPI ANSI/ASME B1.1

20-UN - Unified Extra Fine Thread, which is used for special purposes.
The flank angle is 60°.

Nominal
Diameter
Major
Diameter
Inch
Major
Diameter
mm
Tapping
Drill Size
mm
TPI Pitch
mm
5/16" - 20-UN 0.3125 7.9380 6.700 20 1.270
3/8" - 20-UN 0.3750 9.5250 8.300 20 1.270
9/16" - 20-UN 0.5625 14.288 13.100 20 1.270
5/8" - 20-UN 0.6250 15.875 14.670 20 1.270
11/16" - 20-UN 0.6875 17.462 16.250 20 1.270
1 1/16" - 20-UN 1.0625 26.987 25.800 20 1.270
1 1/8" - 20-UN 1.1250 28.575 27.370 20 1.270
1 3/16" - 20-UN 1.1875 30.162 28.970 20 1.270
1 1/4" - 20-UN 1.2500 31.750 30.550 20 1.270
1 5/16" - 20-UN 1.3125 33.337 32.150 20 1.270
1 3/8" - 20-UN 1.3750 34.925 33.700 20 1.270
1 7/16" - 20-UN 1.4375 36.512 35.320 20 1.270
1 1/2" - 20-UN 1.5000 38.100 36.890 20 1.270
1 9/16" - 20-UN 1.5625 39.688 38.490 20 1.270
1 5/8" - 20-UN 1.6250 41.275 40.080 20 1.270
1 11/16" - 20-UN 1.6875 42.862 41.680 20 1.270
1 3/4" - 20-UN 1.7500 44.450 43.250 20 1.270
1 13/16" - 20-UN 1.8125 46.037 44.840 20 1.270
1 7/8" - 20-UN 1.8750 47.625 46.420 20 1.270
1 15/16" - 20-UN 1.9375 49.212 48.000 20 1.270
2" - 20-UN 2.0000 50.800 49.580 20 1.270
2 1/8" - 20-UN 2.1250 53.975 52.780 20 1.270
2 1/4" - 20-UN 2.2500 57.150 56.030 20 1.270
2 3/8" - 20-UN 2.3750 60.325 59.120 20 1.270
2 1/2" - 20-UN 2.5000 63.500 62.300 20 1.270
2 5/8" - 20-UN 2.6250 66.675 65.470 20 1.270
2 3/4" - 20-UN 2.7500 69.850 68.670 20 1.270
2 7/8" - 20-UN 2.8750 73.025 71.820 20 1.270
3" - 20-UN 3.0000 76.200 75.000 20 1.270