Countersunk Self-Tapping Screws No.4–12 — A4 316 Marine, Packs of 20 or 50

Why choose these A4 marine countersunk self-tapping screws

Countersunk (flat) head self-tapping screws in A4 marine grade 316 stainless steel — driven with a Phillips bit, they sink flush into a countersunk hole for a clean finished surface. The hardened thread cuts its own mate as you drive, working in timber, drywall, plastic and thin sheet without a tapping operation. A4 stainless resists saltwater and chloride attack, so they keep their finish in marine, coastal and outdoor jobs.

Sizes available

Five gauges — No.4 (2.9mm), No.6 (3.5mm), No.8 (4.2mm), No.10 (4.8mm) and No.12 (5.5mm) — across ten length options from 13mm up to 80mm. Choose a length that lets the threaded portion fully engage into the second piece of material for a strong joint.

Pack options

Every size comes as a pack of 20 or a trade pack of 50. The 50 works out between roughly 30% and 50% cheaper per screw, so it is worth taking if you are fitting out a boat or working through a batch of joinery. Mix sizes in one checkout to qualify for free UK delivery on orders over £20.

Typical uses

Boat fit-outs and cabin trim, outdoor furniture, decking trim, soffit and fascia work, drywall and panelling, plywood and hardwood joinery, garden machinery, signage and any surface where a flush-fitting stainless screw is needed.

How to fit

Counterbore the top piece with a countersink bit so the screw head sits flush, then pilot-drill the second piece to the recommended size for the gauge (usually around 0.7× the screw OD for sheet; slightly smaller in hardwood). Drive with a Phillips bit of the correct size (PH2 for most sizes, PH3 for No.12) keeping the bit fully seated to avoid rounding the recess.

Delivery

Same-day dispatch on orders placed before 2pm — free UK delivery on orders over £20.