#12 wood screw
5.5 mm shank
#12 gauge · 0.22 in · pilot 3.6 mm softwood / 4.2 mm hardwood · clearance 5.5 mm
What a #12 is for
Structural fixings, gate hardware and heavy brackets. At 5.5 mm it needs a pilot hole in anything harder than pine.
Two holes, not one
A screw joining two boards needs different holes in each. The clearance hole goes in the top piece at 5.5 mm, wide enough that the thread passes straight through without gripping. The pilot hole goes in the bottom piece at 3.6 mm for softwood or 4.2 mm for hardwood, so the thread has something to bite.
Get this wrong and the failure is specific: drill a pilot-sized hole in both boards and the thread grips the top one too, so instead of pulling the pieces together the screw jacks them apart. The gap that opens is usually blamed on the clamping, and no amount of extra torque closes it.
| Hole | Where | Size | Why |
|---|---|---|---|
| Clearance | Top board | 5.5 mm | Thread passes through freely |
| Pilot, softwood | Bottom board | 3.6 mm | About two thirds of the shank |
| Pilot, hardwood | Bottom board | 4.2 mm | About three quarters — hardwood splits |
The numbers
| Gauge | #12 |
| Shank diameter | 5.5 mm · 0.22 in |
| Nearest metric screw | 5.5 mm |
| Common lengths | 25, 30, 40, 50, 60, 75 mm |
A screw wants at least two thirds of its length in the receiving board. Longer than that adds nothing; shorter and the joint relies on the top board's threads, which are not meant to be carrying it.
Nearby gauges
| Gauge | Shank | Pilot, soft | Pilot, hard | Clearance |
|---|---|---|---|---|
| #8 | 4.2 mm | 2.8 mm | 3.2 mm | 4.5 mm |
| #10 | 4.8 mm | 3.2 mm | 3.6 mm | 5 mm |
| #12 | 5.5 mm | 3.6 mm | 4.2 mm | 5.5 mm |
| #14 | 6.1 mm | 4.2 mm | 4.5 mm | 6.5 mm |
Frequently asked questions
What diameter is a #12 wood screw?
5.5 mm across the shank (0.22 inches). Gauge is a straight line — diameter in inches is 0.060 + 0.013 × gauge — so #12 works out at 0.22.
What pilot hole for a #12 screw?
3.6 mm in softwood, 4.2 mm in hardwood. The pilot is roughly two thirds of the shank in pine and three quarters in oak, because hardwood fibres will not compress and the board splits instead.
What clearance hole for a #12?
5.5 mm — just over the shank, so the thread passes through without biting. This hole goes in the top board only. Drilling a pilot hole in both pieces is what makes a joint spring apart rather than pull together.
What is a #12 screw in metric?
Closest to a 5.5 mm screw at 5.5 mm actual. Metric screws are sold by their real shank diameter, so the number means something — which gauge numbers do not.