Screw Size Equivalents


Click the scope to return to this page

Not really computers or electronics at all, but I find it useful to know what is equal to what when buying screws.
This information is for guidance only and relates primarily to wood screws, not machine screws, nuts & bolts etc.

(Metric measurements are in mm and imperial in inches, all sizes are approximate)


Diameter

Common Lengths Clearance Hole Pilot Hole
Gauge Metric Imperial Metric Imperial Metric Imperial Metric
2 2.0 1/4 - 1/2 6.5 - 13 3/32 2.5 1/16 1.6
3 2.5 3/8 - 1 10 - 25 7/64 3.0 1/16 1.6
4 3.0 1/4 - 11/2 6.5 - 38 1/8 3.5 5/64 2.0
6 3.5 3/8 - 21/2 10 - 65 5/32 4.0 5/64 2.0
8 4.0 3/8 - 31/2 10 - 90 3/16 5.0 3/32 2.5
10 5.0 1/2 - 4 13 - 100 7/32 5.75 1/8 3.5
12 5.5 3/4 - 5 19 - 125 1/4 6.5 1/8 3.5
14 6.5 11/4 - 6 32 - 150 1/4 6.5 5/32 4.0


BA Screwsize Metric outside diameter (mm)
8 2.2
7 2.5
6 2.8
5 3.2
4 3.6
3 4.1
2 4.7
1 5.3
0 6.0

It is increasingly common to find metric screws on sale.
Although a simple concept it causes me great confusion, and doing a reasonably accurate conversion  to decide upon equivalents invariably ends up with a box of screws the wrong length.

The following diagram helps no end. Metric lengths are shown in blue, and imperial lengths in green. The bars are drawn to scale to help make clear that 25mm is pretty close to 1", but an 80mm screw may well break through a piece of 3" timber.