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Formula for Tap Drill Size
1. Select Size Type
Screw (#)
Fractional (")
Metric (mm)
2. Select Machine Screw Size
NC (coarse)
NF (fine)
#0 - 80 NF
#1 - 64 NC
#1 - 72 NF
#2 - 56 NC
#2 - 64 NF
#3 - 48 NC
#3 - 56 NF
#4 - 40 NC
#4 - 48 NF
#5 - 40 NC
#5 - 44 NF
#6 - 32 NC
#6 - 40 NF
#8 - 32 NC
#8 - 36 NF
#10 - 24 NC
#10 - 32 NF
#12 - 24 NC
#12 - 28 NF
2. Select Fractional Size/TPI
NC (coarse)
NF (fine)
1/4 - 20 NC
1/4 - 28 NF
5/16 - 18 NC
5/16 - 24 NF
3/8 - 16 NC
3/8 - 24 NF
7/16 - 14 NC
7/16 - 20 NF
1/2 - 13 NC
1/2 - 20 NF
9/16 - 12 NC
9/16 - 18 NF
5/8 - 11 NC
5/8 - 18 NF
3/4 - 10 NC
3/4 - 16 NF
7/8 - 9 NC
7/8 - 14 NF
1" - 8 NC
1" - 12 NF
1-1/8 - 8 NC
1-1/8 - 12 NF
1-1/4 - 7 NC
1-1/4 - 12 NF
1-3/8 - 6 NC
1-3/8 - 12 NF
1-1/2 - 6 NC
1-1/2 - 12 NF
1-3/4 - 5 NC
2 - 4-1/2 NC
2. Select Metric Size
Coarse Thread
Fine Thread
M3.0 x 0.60
M3.0 x 0.50
M4.0 x 0.70
M4.0 x 0.50
M5.0 x 0.90
M5.0 x 0.80
M8.0 x 1.25
M8.0 x 1.0
M10 x 1.50
M10 x 1.25
M12 x 1.75
M12 x 1.25
M14 x 2.0
M14 x 1.25
M16 x 2.0
M16 x 1.5
M18 x 2.5
M18 x 1.5
M20 x 2.5
M20 x 1.5
M22 x 2.5
M22 x 1.5
M24 x 3.0
M24 x 2.0
3. Percent of Full Thread
65%
75%
(Standard)
80%
Theoretical Drill Size
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Nearest Fractional Size
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Nearest Size (Any)
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