STI Drill Size
Tap Drill Sizes - STI Taps - Inch
Minor Diameter (After Tapping) (in)
Tap Drill Diameter (in)
Threads Per Inch
Tap Size
Steel, Magnesium, Plastic
UNC
UNF
Min
Max
Aluminum
2 3 4 5 6
56 48
– –
0.0899 0.1036 0.1029 0.1175 0.1166 0.1305 0.1448 0.1435 0.1708 0.1701 0.1990 0.1968 0.2250 0.2608 0.2577 0.3245 0.3215 0.3885 0.3840 0.4530 0.4483 0.5166 0.5108 0.5806 0.5745 0.6447 0.6370 0.7716 0.7635 0.8990 0.8905 1.0271
0.0961 0.1104 0.1086 0.1252 0.1229 0.1373 0.1527 0.1503 0.1781 0.1771 0.2080 0.2041 0.2340 0.2704 0.2646 0.3342 0.3288 0.3987 0.3910 0.4639 0.4561 0.5273 0.5186 0.5918 0.5826 0.6564 0.6451 0.7838 0.7720 0.9119 0.8994 1.0421
0.0938 0.1065 0.1040 0.1200 0.1181 0.1339 0.1470 0.1470 0.1730 0.1730 0.2031 0.2010 0.2280 0.2660 0.2610 0.3320 0.3281 0.3970 0.3906 0.4531 0.4531 0.5156 0.5156 0.5781 0.5781 0.6562 0.6406 0.7812 0.7656 0.9062 0.8906 1.0312
0.0960 0.1094 0.1065 0.1200 0.1200 0.1360 0.1495 0.1495 0.1770 0.1770 0.2055 0.2031 0.2280 0.2660 0.2638 0.3320 0.3281 0.3970 0.3906 0.4531 0.4531 0.5156 0.5156 0.5938 0.5781 0.6562 0.6406 0.7812 0.7656 0.9062 0.8906 1.0312
–
56
40
–
–
48
40 32
– –
–
40
32
–
8
–
36
24
–
10 12
–
32
24 20
– –
1/4
–
28
18
–
5/16
–
24
16
–
3/8
–
24
14
–
7/16
–
20
13
–
1/2
–
20
12
–
9/16
–
18
11
–
5/8
–
18
10
–
3/4
– 9 – 8
16
–
7/8
14
–
1"
– 1.0312 The suggested drill sizes for aluminum listed in the table are within the minor diameter limits for STI tapped holes specified in MS 33537. Alternate drill sizes are suggested in many instances for magnesium, steel and plastics to provide for maximum tap wear life. In the case of magnesium, the larger size is recommended to allow for material close-in. There are suggested drill sizes and any special requirements or specifications will supersede these recommendations. 12 1.0181 1.0281 1.0156
Threading Technical
785
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