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Screw pilot drill charts
Not being an accomplished woodworker, I was always puzzled by what pilot drill I should use for a given screw size. I ran across the attached chart somewhere and, finding it useful, thought I should pass it along to others puzzled by the mysteries of the brown stuff.
Later on I ran across a similar chart for self-tapping sheet metal screws and have included that as well.
Code:
WOOD SCREW DATA
N = NOMINAL SIZE
T = THREADS PER INCH
D = DIAMETER OF UNTHREADED ROOT (in)
B = BODY DRILL SIZE (in)
S = PILOT DRILL SIZE IN SOFT WOOD (in)
H = PILOT DRILL SIZE IN HARD WOOD (in)
N T D B S H B S H
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0 32 .060 52 75 66
1 28 .073 47 71 57
2 26 .086 42 65 54
3 24 .099 37 58 53
4 22 .112 32 55 51 1/8 1/16 5/64
5 20 .125 30 53 47 9/64 5/64 3/32
6 18 .138 27 52 44 9/64 5/64 3/32
7 16 .151 22 51 39 5/32 3/32 7/64
8 15 .164 18 48 35 11/64 3/32 7/64
9 14 .177 14 45 33 3/16 7/64 1/8
10 13 .190 10 43 31 3/16 7/64 1/8
11 .203 4 40 29
12 11 .216 2 38 25 7/32 1/8 5/32
14 10 .242 D 32 14
16 9 .268 I 29 10
18 8 .294 N 26 6
20 8 .320 P 19 3
24 7 .372 V 15 D
Recommended Drill Sizes for Self-Tapping Screws (Sheet Metal)
N = Number
T = Threads per inch
OD = Outside Diameter
A = Drill for heavy metals
B = Drill for light metals
N T OD A B
2 32 .086 49 49
4 24 .112 41 41
5 20 .125 36 36
6 20 .138 32 32
7 19 .151 30 30
8 18 .164 28 29
10 16 .190 20 21
12 14 .216 13 14
1/4 14 .250 3 4
5/16 12 .313 I H
3/8 12 .375 R Q