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 |
|
*DRILL
SIZES FOR |
Tap Size |
**DRILL SIZES FOR |
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|
Diameter |
Threads Per Inch | |||||
|
Drill Size |
Decimal |
UNC |
UNF |
Drill Size |
Decimal |
|
|
56 |
.0465 |
0 |
80 |
3/64 |
.0469 | |
|
53 |
.0595 |
1 |
64 |
53 |
.0595 |
|
|
53 |
.0595 |
72 |
53 |
.0595 |
||
|
51 |
.0670 |
2 |
56 |
50 |
.0700 |
|
|
50 |
.0700 |
64 |
49 |
.0730 |
||
|
48 |
.0760 |
3 |
48 |
46 |
.0810 |
|
|
46 |
.0810 |
56 |
45 |
.0820 |
||
|
44 |
.0860 |
4 |
40 |
43 |
.0890 |
|
|
43 |
.0890 |
48 |
42 |
.0935 |
||
|
39 |
.0995 |
5 |
40 |
38 |
.1015 |
|
|
38 |
.1015 |
44 |
37 |
.1040 |
||
|
36 |
.1065 |
6 |
32 |
7/64 |
.1094 |
|
|
33 |
.1130 |
40 |
32 |
.1160 |
||
|
29 |
.1360 |
8 |
32 |
29 |
.1360 |
|
|
29 |
.1360 |
36 |
28 |
.1405 |
||
|
26 |
.1470 |
10 |
24 |
24 |
.1520 |
|
|
5/32 |
.1562 |
32 |
21 |
.1590 |
||
|
11/64 |
.1719 |
12 |
24 |
16 |
.1770 |
|
|
15 |
.1800 |
28 |
14 |
.1820 |
||
|
8 |
.1990 |
1/4 |
20 |
6 |
.2040 |
|
|
3 |
.2130 |
28 |
7/32 |
.2188 |
||
|
F |
.2570 |
5/16 |
18 |
14/64 |
.2656 |
|
|
I |
.2720 |
24 |
J |
.2770 |
||
|
5/16 |
.3125 |
3/8 |
16 |
P |
.3230 |
|
|
Q |
.3320 |
24 |
R |
.3390 |
||
|
U |
.3680 |
7/16 |
14 |
3/8 |
.3750 |
|
|
W |
.3860 |
20 |
25/64 |
.3906 |
||
|
27/64 |
.4219 |
1/2 |
13 |
7/16 |
.4375 |
|
|
29/64 |
.4531 |
20 |
29/64 |
.4531 |
||
|
31/64 |
.4844 |
9/16 |
12 |
1/2 |
.5000 |
|
|
1/2 |
.5000 |
18 |
33/64 |
.5156 |
||
|
17/32 |
.5312 |
5/8 |
11 |
35/64 |
.5469 |
|
|
9/16 |
.5625 |
18 |
37/64 |
.5781 |
||
|
21/32 |
.6562 |
3/4 |
10 |
43/64 |
.6719 |
|
|
11/16 |
.6875 |
16 |
45/364 |
.7031 |
||
|
49/64 |
.7656 |
7/8 |
9 |
25/32 |
.7812 |
|
|
51/64 |
.7969 |
14 |
13/16 |
.8125 |
||
|
7/8 |
.8750 |
1 |
8 |
57/64 |
.8906 |
|
|
59/64 |
.9219 |
12 |
15/16 |
.9375 |
||
|
*Drill sizes
recommended for "Free Cutting Materials" produces 65-75% of
thread. |
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TAPPING TIPS Strength of tapped holes: Strength tests show that any increase over 60% of thread for the tapped holes does not increase static strength of fastening. Bolts break at 55% of engagement. Tapping blind holes: Drill hole deep enough to accommodate chips. Tap breakage: If difficulty or breakage occurs, check drill size in view of material hardness and make sure tap is sharp. Breaking small drills: Small drills (1/8" and under) break easily when they are not run at high speeds. Difficulty in drilling: If starting drill is difficult, thinning web of drill at the point solves this problem. Class of fit: Most commercial bolts and screws are made to fit 2A external thread standards, which fit with 2B tapped threads. |
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