Specifications of International Thread Standards

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
TPIPitch
mm
5/16" - 20-UN0.31257.93806.700201.270
3/8" - 20-UN0.37509.52508.300201.270
9/16" - 20-UN0.562514.28813.100201.270
5/8" - 20-UN0.625015.87514.670201.270
11/16" - 20-UN0.687517.46216.250201.270
1 1/16" - 20-UN1.062526.98725.800201.270
1 1/8" - 20-UN1.125028.57527.370201.270
1 3/16" - 20-UN1.187530.16228.970201.270
1 1/4" - 20-UN1.250031.75030.550201.270
1 5/16" - 20-UN1.312533.33732.150201.270
1 3/8" - 20-UN1.375034.92533.700201.270
1 7/16" - 20-UN1.437536.51235.320201.270
1 1/2" - 20-UN1.500038.10036.890201.270
1 9/16" - 20-UN1.562539.68838.490201.270
1 5/8" - 20-UN1.625041.27540.080201.270
1 11/16" - 20-UN1.687542.86241.680201.270
1 3/4" - 20-UN1.750044.45043.250201.270
1 13/16" - 20-UN1.812546.03744.840201.270
1 7/8" - 20-UN1.875047.62546.420201.270
1 15/16" - 20-UN1.937549.21248.000201.270
2" - 20-UN2.000050.80049.580201.270
2 1/8" - 20-UN2.125053.97552.780201.270
2 1/4" - 20-UN2.250057.15056.030201.270
2 3/8" - 20-UN2.375060.32559.120201.270
2 1/2" - 20-UN2.500063.50062.300201.270
2 5/8" - 20-UN2.625066.67565.470201.270
2 3/4" - 20-UN2.750069.85068.670201.270
2 7/8" - 20-UN2.875073.02571.820201.270
3" - 20-UN3.000076.20075.000201.270
20-UN Thread