Fabrication

Tapping and Clearance Drills for Fractional Machine Screws

Screw Size Tapping Drills Clearance Drills
Nom. Dia. (in)Threads
/Inch
SeriesDec. Equiv. Drill Size
(65-75% thread)
Equivalents Close FitFree Fit
(decimal)(mm) Drill SizeDec. Equiv.Drill SizeDec. Equiv.
1/1664NS0.0625 3/64"0.04691.1913 520.0635510.0670
72NS 3/64"0.04691.1913
5/6460NS0.0781 1/16"0.06251.5875 460.0810450.0820
72NS 520.06351.6129
3/3248NS0.0938 490.07301.8542 410.0960400.0980
50NS 490.07301.8542
7/6448NS0.1094 430.08902.2606 340.1110320.1160
1/832NS0.1250 3/32"0.09382.3825 300.1285290.1360
40NS 380.10152.5781
9/6440NS0.1406 320.11602.9464 270.1440260.1470
5/3232NS0.1563 1/8"0.12503.1750 200.1610190.1660
36NS 300.12853.2639
11/6432NS0.1719 9/64"0.14063.5712 160.1770150.1800
3/1624NS0.1875 260.14703.7338 110.191090.1960
32NS 220.15703.9878
13/6424NS0.2031 200.16104.0894 40.209030.2130
7/3224NS0.2188 160.17704.4958 20.221010.2280
32NS 120.18904.8006
15/6424NS0.2344 100.19354.9149 C0.2420D0.2460
1/420NC0.2500 70.20105.1054 F0.2570H0.2660
24NS 40.20905.3086
27NS 30.21305.4102
28NF 30.21305.4102
32NEF 7/32"0.21885.5575
5/1618NC0.3125 F0.25706.5278 P0.3230Q0.3320
20NS 17/64"0.26566.7462
24NF I0.27206.9088
27NS J0.27707.0358
32NEF 9/32"0.28127.1425
3/816NC0.3750 5/16"0.31257.9375 W0.3860X0.3970
20NS 21/64"0.32818.3337
24NF Q0.33208.4328
27NS R0.33908.6106
32NEF 11/32"0.3438"8.7325
7/1614NC0.4375 U0.36809.3472 29/64"0.453115/32"0.4687
20NF 25/64"0.39069.9212
24NS X0.397010.0838
27NS Y0.404010.2616
28NEF 15/32"0.468811.9075
1/212NS0.5000 27/64"0.421910.7163 33/64"0.515617/32"0.5312
13NC 27/64"0.421910.7163
20NF 29/64"0.453111.5087
24NS 29/64"0.453111.5087
27NS 15/32"0.468811.9075
28NEF 15/32"0.468811.9075
9/1612NC0.5625 31/64"0.484412.3038 37/64"0.578119/32"0.5938
18NF 33/64"0.515613.0962
24NEF 33/64"0.515613.0962
27NS 17/32"0.531313.4950
5/811NC0.6250 17/32"0.531313.4950 41/64"0.640621/32"0.6562
12NS 35/64"0.546913.8913
18NF 37/64"0.578114.6837
24NEF 37/64"0.578114.6837
27NS 19/32"0.593715.0800
11/1611NS0.6875 19/32"0.593715.0800 45/64"0.703123/32"0.6562
16NS 5/8"0.625015.8750
24NEF 41/64"0.640616.4084
3/410NC0.7500 21/32"0.656216.6675 49/64"0.765625/32"0.7812
12NS 43/64"0.671917.0663
16NF 11/16"0.687517.4625
20NEF 45/64"0.703117.8587
27NS 23/32"0.718718.2550
13/1610NS0.8125 23/32"0.718718.2550 53/64"0.828127/32"0.8438
20NEF 49/64"0.765619.4462
7/89NC0.8750 49/64"0.765619.4462 57/64"0.890629/32"0.9062
12NS 51/64"0.796920.2413
14NF 13/16"0.812520.6375
18NS 53/64"0.828121.0337
20NEF 53/64"0.828121.0337
27NS 27/32"0.843721.4300
15/169NS0.9375 53/64"0.828121.0337 61/64"0.953131/32"0.9688
20NEF 57/64"0.890622.6212
18NC1.0000 7/8"0.875022.2250 1-1/64"1.01561-1/32"1.0313
12NF 59/64"0.921923.4163
14NS 15/16"0.937523.8125
20NEF 61/64"0.953124.2087
27NS 31/32"0.968724.6050
32* 31/32"0.968724.6050
1-1/1618NEF1.0625 1"1.000025.4000 1-5/64"1.07811-3/32"1.0938
1-1/87NC1.1250 63/64"0.984425.0038 1-9/64"1.14061-5/32"1.1562
12NF 1-3/64"1.046926.5913
18NEF 1-1/16"1.062526.9875
1-3/1618NEF1.1875 1-1/8"1.125028.5750 1-13/64"1.20311-7/32"1.2188
1-1/47NC1.2500 1-7/64"1.109428.1788 1-17/64"1.26561-9/32"1.2812
12NF 1-11/64"1.171929.7663
18NEF 1-3/16"1.187530.1625
1-5/1618NEF1.3125 1-1/4"1.250031.7500 1-21/64"1.32811-11/32"1.3438
1-3/86NC1.3750 1-7/32"1.218830.9575 1-25/64"1.39061-13/32"1.4062
12NF 1-19/64"1.296932.9413
18NEF 1-5/16"1.312533.3375
1-7/1618NEF1.3693 1-3/8"1.375034.9250 1-29/64"1.45311-15/32"1.4688
1-1/26NC1.5000 1-11/32"1.343834.1325 1-33/64"1.51561-17/32"1.5312
12NF 1-27/64"1.421936.1163
18NEF 1-7/16"1.437536.5125
1-9/1618NEF1.5625 1-1/2"1.500038.1000 1-37/64"1.57811-19/32"1.5938
1-5/85 1/2NS1.6250 1-29/64"1.453136.9087 1-41/64"1.64061-21/32"1.6562
18NEF 1-9/16"1.562539.6875
1-11/1618NEF1.6875 1-5/8"1.625041.2750 1-45/64"1.70311-23/32"1.7188
1-3/45NC1.7500 1-9/16"1.562539.6875 1-49/64"1.76591-25/32"1.7812
1-7/85NS1.8750 1-11/16"1.687542.8625



24 1/2NC2.0000 1-25/32"1.781345.2450



Nom. Dia. (in)Threads
/Inch
SeriesDec. Equiv. Drill Size
(65-75% thread)
(decimal)(mm) Drill SizeDec. Equiv.Drill SizeDec. Equiv.
Equivalents Close FitFree Fit
Screw Size Tapping Drills Clearance Drills

* The thread size of a C-mount camera lens.


Notes

Thread Series
National Coarse (NC)
National Fine (NF)
National Extra Fine (NEF)
National Special (NS)

1 inch = 25.4 millimeters

Tap Drill Size (65-75% thread) = Nominal Diameter - One Pitch Length
example:  Tap Drill for 1/4-20 NC screw is #7, closest drill to 0.2000 inches (0.2000 = 0.2500 - 0.0500)
Pitch (in.) = 1 / (Threads per Inch)
example:  Pitch of 20 Threads per Inch is 0.0500 inches (0.0500 = 1/20)

Other Resources


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DISCLAIMER

Page author: Dawn Rorvik (rorvikd@evergreen.edu)
Last modified: 05/20/2003