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Tap-Drill Selector Chart

*DRILL SIZES FOR Free Cutting Metals Steel, Aluminum Copper and Copper Alloys
Drill Size Decimal
56 .0465
53 .0595
53 .0595
51 .0670
50 .0700
48 .0760
48 .0760
44 .0860
43 .0890
39 .0995
38 .1015
36 .1065
33 .1130
29 .1360
29 .1360
26 .1470
5/32 .1562
11/64 .1719
15 .1800
8 .1990
3 .2130
F .2570
I .2720
5/16 .3125
Q .3320
W .3860
27/64 .4219
31/64 .4844
1/2 .5000
17/32 .5312
9/16 .5625
21/32 .6562
11/16 .6875
49/64 .7656
51/64 .7969
7/8 .8750
59/64 .9219
*Drill sizes recommended for "Free Cutting Materials" produces 65-75% of thread.
**For "Hard or Rough Materials", 60-70% of thread.
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.
Tap Size
Diameter Threads Per Inch
UNC UNF
0   80
1 64  
  72
2 56  
  64
3 48  
  46
4 40  
  48
5 40  
  44
6 32  
  40
8 32  
  36
10 24  
  32
12 24  
  28
1/4 20  
  28
5/16 18  
  24
3/8 16  
  24
7/16 14  
  20
1/2 13  
  20
9/16 12  
  18
5/8 11  
  18
3/4 10  
  16
7/8 9  
  14
1 8  
  12
*Drill sizes recommended for "Free Cutting Materials" produces 65-75% of thread.
**For "Hard or Rough Materials", 60-70% of thread.
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.
**DRILL SIZES FOR Hard or Tough Metals Carbon & Alloy Steel, Heat Treated Steels, Stnls Steels
Drill Size Decimal
3/64 .0469
53 .0595
53 .0595
50 .0700
49 .0730
46 .0810
45 .0820
43 .0890
42 .0935
38 .1015
37 .1040
7/64 .1094
32 .1160
29 .1360
28 .1405
24 .1520
21 .1590
16 .1770
14 .1820
6 .2040
7/32 .2188
14/64 .2656
J .2770
P .3230
R .3390
3/8 .3750
25/64 .3906
7/16 .4375
29/64 .4531
1/2 .5000
33/64 .5156
35/64 .5469
37/64 .5781
43/64 .6719
45/364 .7031
25/32 .7812
13/16 .8125
57/64 .8906
15/16 .9375
*Drill sizes recommended for "Free Cutting Materials" produces 65-75% of thread.
**For "Hard or Rough Materials", 60-70% of thread.
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.