Wood Screw Pilot Hole Sizes

When joining wood with screws, it is necessary to bore pilot holes. Pilot holes make screws easier to drive and there is less chance of damaging the screws or wood. Bore holes large enough to freely accommodate the screw shank in the first piece of wood. Bore holes slightly smaller than the thread diameter, to a depth of half the length of the threaded portion in the second piece of wood.

No. of
Screw		 Pilot Holes (A) Shank Clearance Holes (B) Counter
sink (C)
Hardwoods Softwoods Twist bit
(Nearest size
in fractions
of an inch		 Drill
Gauge No.
or Letter
To be used
for maximum
holding power		 No. of
Auger Bit
To counterbore
for sinking head
(by 1/16ths)
Twist bit
(Nearest size
in fractions
of an inch)		 Drill
Gauge No.
To be used
for maximum
holding power
 Twist bit
(Nearest size
in fractions
of an inch)		 Drill
Gauge No.
To be used
for maximum
holding power
6 - 44 1/16 52 9/64 27 5
7 - 39 1/16 51 5/32 22 5
8 7/64 35 5/64 48 11/64 18 6
9 7/64 33 5/64 45 3/16 14 6
10 1/8 31 3/32 43 3/16 10 6
11 - 29 3/32 40 13/64 4 7
12 - 25 7/64 38 7/32 2 7
14 3/32 14 7/64 32 1/4 D 8
16 - 10 9/64 29 17/64 I 9
18 13/64 6 9/64 26 19/64 N 10

Plate 6B - Wood Screw Chart



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