Wood screws

Wood screws have a sharp point, coarse threads, and a shank that may be unthreaded near the head. They are designed to pull two pieces of wood together — the threads bite into the receiving piece while the shank slides freely through the top piece.

Common screw number sizes and diameters

Screw #	Major diameter	Pilot hole (hardwood)	Pilot hole (softwood)
#4	3.0 mm (0.112")	2.4 mm	2.0 mm
#6	3.5 mm (0.138")	2.8 mm	2.2 mm
#8	4.2 mm (0.164")	3.4 mm	2.7 mm
#10	4.8 mm (0.190")	4.0 mm	3.1 mm
#12	5.5 mm (0.216")	4.5 mm	3.5 mm

Head styles

Head style	Description	When to use
Flat (countersunk)	Angled underhead, sits flush with surface	Most general woodworking
Pan	Low rounded head, larger bearing surface	When a protruding head is acceptable
Round	Domed head, no countersink	Decorative applications
Oval	Flat with rounded top	Finish work with visible head

Drive types

Phillips #2 — most common; designed to cam out at high torque (protects the work surface, but frustrating when overtightening is the goal)
Square / Robertson — less cam-out than Phillips; very common in Canada
Torx / Star (T20, T25) — high torque transfer, low cam-out; increasingly common in construction screws and decking

Materials

Zinc-plated steel — interior use only; will rust if exposed to moisture
Stainless steel — exterior and marine applications; Type 304 for general outdoor, Type 316 for saltwater
Galvanized — hot-dip galvanized for deck ledgers and pressure-treated lumber contact
Coated (ACQ compatible) — required when fastening to ACQ pressure-treated lumber, which reacts with zinc plating

Common mistakes

No pilot hole in hardwood → splitting, especially near the end grain
Wrong material (zinc-plated indoors-only screws in exterior or pressure-treated applications) → rust failure within 2–3 years
Overdriving flat-head screws without a countersink → tears the wood face

Wood screw assortments
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