The table below is a guide to show metric equivalents of common Imperial screw gauges. The table contains data on Head diameter and Countersink drill size, Shank diameter and Clearance drill size, Pilot hole sizes for Timber, Rawlplug colours and Masonry drill sizes

Imperial Metric Screw Screw Head Screw Screw Shank Softwood Hardwood Masonry
Screw Screw Head Dia Countersink Shank Dia Clearance Pilot Dia Pilot Dia Plug Drill
Gauge No. Guage mm mm Drill mm
mm Drill mm mm mm Colour mm
2 2 4.36 6.0 2.38 2.5 1.5 1.5
3 2.5 5.16 6.0 2.77 3.0 1.5 1.5 Yellow 5
4 3 5.95 6.0 2.77 3.0 1.5 2.0 Yellow 5
6 3.5 7.14 8.0 3.57 4.0 2.0 2.5 Red 6
8 4 8.73 9.0 3.97 4.5 2.5 3.0 Red/Brown 6 or 7
10 5 9.92 10.0 4.76 5.5 3.0 3.0 Brown 7
12 5.5 11.11 11.0 5.55 6.5 3.0 3.5 Brown 7
14 6.5 12.70 12.0
6.35 7.0 3.5 4.0 Blue 10


Wood Screw Dimensions, Sizes, Head Diameters & Threads per Inch
Nominal
Screw
Size 		Threads
per
Inch 		Basic Diameter
of Screw 		Average Head Diameter
Flat & Oval Round
Decimal Fraction Decimal Fraction Decimal Fraction
0 32 0.060 1/16 0.109 7/64 0.106 7/64
1 28 0.073 5/64 0.135 9/64 0.130 1/8
2 26 0.086 3/32 0.160 5/32 0.154 5/32
3 24 0.099 3/32 0.185 3/16 0.178 11/64
4 22 0.112 7/64 0.210 13/64 0.202 13/64
5 20 0.125 1/8 0.236 15/64 0.227 7/32
6 18 0.138 9/64 0.262 17/64 0.250 1/4
7 16 0.151 5/32 0.287 9/32 0.275 9/32
8 15 0.164 5/32 0.312 5/16 0.298 19/64
9 14 0.177 11/64 0.337 11/32 0.323 21/64
10 13 0.190 3/16 0.363 23/64 0.347 11/32
12 11 0.216 7/32 0.414 13/32 0.395 25/64
14 10 0.242 15/64 0.480 31/64 0.443 7/16
16 9 0.268 17/64 0.515 33/64 0.491 31/64
18 8 0.294 19/64 0.602 19/32 0.539 17/32
20 8 0.320 5/16 0.616 39/64 0.587 19/32
24 7 0.372 3/8 0.724 23/32 0.683 11/16