Screw Thread Pitches and Tap Drill Sizes

Screw Thread Size and Pitch Outside Diameter of Screw (in.) Tap Drill Size Decimal Equivalentof Drill Size
National Coarse (NC) Series
No. 1-64 0.073 53 0.0595
No. 2-56 0.086 50 0.0700
No. 3-48 0.099 47 0.0785
No. 4-40 0.112 43 0.0890
No. 5-40 0.125 38 0.1015
No. 6-32 0.138 36 0.1065
No. 8-32 0.164 29 0.1360
NO. 10-24 0.190 25 0.1495
No. 1 2-24 0.216 16 0.1770
No. 1/4-20 0.250 07 0.2010
No. 5/16-18 0.3125 UL 0.2570
No. 3/8-16 0.375 5/16 0.3125
No. 7/16-14 0.4375 U 0.3680
No. 1/2-13 0.500 27/64 0.4219
No. 9/16-12 0.5625 31/64 0.4843
No. 5/8-11 0.625 17/32 0.5312
No. 3/4-10 0.750 21/32 0.6562
No. 7/8-9 0.875 49/64 0.7656
No. 1-8 1.000 7/8 0.875
National Fine (NF) Series
No. 0-80 0.060 3/64 0.0469
No. 1-72 6.073 53 0.0595
No. 2-64 0.086 50 0.0700
No. 3-56 0.099 45 0.0820
No. 4-48 0.112 42 0.0935
No. 5-44 0.125 37 0.1040
No. 6-40 0.138 33 0.1130
No. 8-36 0.164 29 0.1360
No. 10-32 0.190 21 0.1590
No. 12-18 0.216 14 0.1820
No. 1/4-28 0.250 3 0.2130
No. 5/16-24 0.3125 I 0.2720
No. 3/8-24 0.375 Q 0.3320
No. 7/16-20 0.4375 25/64 0.3906
No. 1/2-20 0.500 29/64 0.4531
No. 9/16-18 0.5625 33/64 0.5156
No. 5/8-18 0.625 37/64 0.5781
No. 3/4-16 0.750 11/16 0.6875
7/8-16 0.875 13/16 0.8125
No. 1-14 1.000 15/16 0.9375
METRIC SERIES
1.6mm x .35 .0630 1.20mm .0472
2.0mm x .40 .0787 1.60mm .0630
2.5mm x .45 .0984 2.05 mm .0807
3.0mm x .50 .1181 2.50mm .0984
3.5mm x .60 .1378 2.90mm .1142
METRIC SERIES
Screw thread size and pitch Outside diameter of screw (in.)
Tap drill size
Decimal equivalent Of drill size
4.0mm x .70 .1575 3.30mm .1299
5.0mm x .80 .1968 4.20 mm .1654
6.3mm x 1.00 .2480 5.30mm .2087
8.0mm x 1.25 .3150 6.80 mm .2677
10.0mm x 1.50 .3937 8.50mm .3346
12.0mm x 1.75 .4724 10.20mm .4016
14.0mm x 2.00 .5512 12.00mm .4724
16.0mm x 2.00 .6299 14.00mm .5512
20.0mm x 2.50 .7874 17.50 mm .6890
24.0mm x 3.00 .9449 21.00mm .8268
30.0mm x 3.50 1.1811 26.50mm 1.0433
36.0mm x 4.00 1.4173 32.00mm 1.2598
42.0mm x 4.50 1.6535 37.50mm 1.4764
48.0mm x 5.00 1.8898 43.00 mm 1.6929
56.0mm x 5.50 2.2047 50.50 mm 1.9882
64.0mm x 6.00 2.5197 58.00mm 2.2837
72.0mm x 6.00 2.8346 66.00mm 2.5984
80.0mm x 6.00 3.1456 74.00mm 2.9134
90.0mm x 6.00 3.5433 84.00mm 3.3071
100mm x 6.00 3.9370 94.00 mm 3.7008
NATIONAL TAPER PIPE THREAD PITCHES AND TAP DRILL SIZES
Nominal thread size (in.) Threads per inch Major pipe diameter (in.) Tape drill size (In.)  Decimal equivalent of drill size (in.)
1/8 27 0.405 21/64 0.32813
1/4 18 0.540 29/64 0.45313
3/8 18 0.675 19/32 0.59375
1/2 14 0.840 23/32 0.71875
3/4 14 1.050 15/16 0.9375
1 11 1/2 1.315 1 3/6 1.1875
1 1/4 11 1/2 1.660 1 15/32 1.46785
1 1/2 11 1/2 1.900 1 23/32 1.71875
2 11 1/2 2.375 2 3/16 2.1875
2 1/2 8 2.875 2 11/16 2.6875
3 8 3.500 3 5/16 3.3125
3 1/2 8 4.00 3 13/16 3.8125
4 8 4.500 4 3/16 4.1875

Table Formulas for calculating the tap drill size for inch and metric threads.

NOTE:This formula will determine a recommended decimal size, then use the numbered, lettered, or to the computed size.

FOR METRIC SIZES:

The recommended tap drill size is equal to the outside diameter minus the pitch. Metric tap sizes are designated by a capital M, the outside diameter in millimeters, and by the pitch in millimeters; such as M22 x 1.5. To find' the recommended tap drill size, subtract 1.5 from 22, to get 20.5, which is the recommended tap drill size. If a metric or inch is not available for the recommended tap drill size, the round up to the nearest available drill.


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