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 ------------------------------------------------------------------------------- 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
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