Wood Screws: Sizes, Types, and Which to Buy for Every Job

A deck built with standard yellow zinc-plated screws starts rusting within weeks of the first rain. Within two years, the screw heads are orange, streaking rust stains down the timber, and losing their grip. Replacing every screw on a 15m2 deck costs more in labour than the deck boards themselves. That's what happens when you grab the wrong box.

Wood screws are the most-used fixing in any timber project, and the choice matters more than most people think. Wrong gauge, wrong length, wrong material for the environment, and you're either splitting timber, watching fixings corrode, or pulling everything apart to redo it.

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What wood screws are and what they do

A wood screw is a steel fastener with a tapered shank, a helical thread that cuts into timber as it's driven, and a shaped head that accepts a driver bit. The thread grips the wood fibres and pulls the two pieces together. Unlike nails, which rely on friction alone, screws create a mechanical lock that resists being pulled apart.

The term "wood screw" covers a broad family. You'll see them sold as multi-purpose screws, chipboard screws, or just "yellow screws" (after their zinc-plated coating). The differences between these labels are mostly marketing. A modern multi-purpose screw from Screwfix or Toolstation works in softwood, hardwood, chipboard, MDF, and sheet materials. It's the universal timber fixing.

Every wood screw has four characteristics that matter: gauge (the diameter of the shank), length, head type, and drive type. Get those four right for the job and the screw does its work quietly for decades. Get them wrong and you'll know about it.

Types, sizes, and specifications

Gauge and length

Gauge is the screw's diameter, measured across the shank in millimetres. The UK market has largely moved to metric sizing, though some older packaging still uses imperial gauge numbers (#6, #8, #10). For practical purposes, you need to know five gauges:

Length is measured from the tip to the top of the head on countersunk screws. Available from 16mm up to 200mm, but 90% of domestic work uses screws between 25mm and 100mm.

The rule for choosing length: the screw should penetrate the second piece of timber by at least twice the thickness of the first piece. Fixing a 22mm floorboard to a joist? You need at least 44mm of screw in the joist, so a 65mm or 75mm screw is right. A 40mm screw wouldn't grip. A 100mm screw is overkill and risks hitting services below.

Head types

Countersunk (CSK) is what you want for almost everything. The head sits flush with or below the timber surface. Double-countersunk heads have a shallower profile that pulls into the wood more cleanly.

Pan head and round head sit proud of the surface. Used for fixing thin sheet materials where a countersunk head would pull through, or for decorative hardware.

Wafer head is a very low-profile head for sheet material (plasterboard, plywood) where you need maximum holding with minimum head projection.

For extension work, buy countersunk. Every time.

Drive types: Pozi vs Torx

PZ2 (Pozidriv) is the UK standard. Every drill kit ships with a PZ2 bit. Every trade van carries a PZ2 bit. Every box of screws at Screwfix and Toolstation from the budget shelf to the premium shelf is available in Pozi drive. It works. It's everywhere.

Torx (star-shaped) is technically better. It transfers more torque, cams out less (that frustrating slip where the bit jumps out of the screw head mid-drive), and gives a more positive feel. Professional joiners who've switched to Torx rarely go back.

The honest position: PZ2 is fine for every job on a domestic project. Torx is better, but you'll pay more per box, you'll need to carry extra bits, and every tradesperson on your site will have Pozi bits already. Don't overthink it.

Thread types

Single thread screws have one spiral running up the shank. Standard, works for everything.

Twin thread (double thread) screws have two spirals, so they drive in twice as fast for the same number of rotations. Most modern multi-purpose screws are twin thread. They're the default now.

Partially threaded screws have a smooth shank below the head. This matters when joining two pieces of timber: the smooth section slides through the top piece while the threaded section grips only the bottom piece, pulling the two together tightly. For fixing floorboards or joining structural timber, partially threaded is the better choice.

Fully threaded screws grip along their entire length. Better for sheet materials and situations where you want holding power along the full depth.

Materials and coatings

This is where people get caught out.

Yellow zinc-plated (the standard "yellow screw") is for interior use only. The zinc coating provides basic corrosion resistance in dry conditions. Use these indoors and they'll last indefinitely. Use them outside and they'll start rusting within days of sustained moisture exposure. A UK-based corrosion test showed visible rust on standard yellow zinc-plated screws within 72 hours of water exposure.

Stainless steel A2 (304) is the correct choice for any permanent exterior fixing. Decking, fences, external cladding, pergolas, garden structures. A2 stainless costs roughly two to three times the price of zinc-plated equivalents, but it won't corrode.

Stainless steel A4 (316) is for coastal environments. If you're within about five miles of the coast, salt spray will attack even A2 stainless over time. A4 is rated for marine exposure.

Galvanised (hot-dip) sits between zinc-plated and stainless for corrosion resistance. Adequate for sheltered exterior use (under soffits, covered porches) at a lower cost than stainless.

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How to work with wood screws

Pilot holes

Modern multi-purpose screws with self-drilling points (thread-cutting tips, wax coatings, serrated threads) genuinely don't need pilot holes in softwood when you're driving into the centre of the timber, well away from edges and ends.

But pilot holes are not optional in these situations:

• Hardwood (oak, ash, beech, iroko). Always.
• Within 25mm of an edge. Always.
• Within 30mm of an end grain. Always.
• Stainless steel or brass screws. These are more brittle than carbon steel. The screw will snap if it meets resistance without a pilot hole.

For softwood, a pilot hole still gives a cleaner result. The screw drives straighter, the timber doesn't swell around the head, and the finished joint looks better. If you're doing visible joinery, drill pilot holes regardless.

The clearance hole matters when joining two pieces. Drill it through the top piece at the same diameter as the screw shank. This lets the screw pull through the top piece freely and clamp the two pieces together. Skip the clearance hole and the thread grips both pieces, leaving a gap between them.

Countersinking

A countersink bit cuts a shallow cone into the timber surface so the screw head sits flush. You can buy combination bits that drill the pilot hole and countersink in a single pass (the Trend Snappy countersink with drill is the one most tradespeople use). These save time and ensure the countersink is centred on the pilot hole.

Without countersinking, a countersunk screw head crushes the wood fibres around it as it's driven home. In softwood this looks ragged. In hardwood it can split the surface.

Driving technique

Use a combi drill or impact driver with the correct bit (PZ2 for most screws, PZ3 for 6mm gauge). Set the clutch on your drill to a sensible torque setting. Too high and you'll overdrive the screw, stripping the hole or pulling the head below the surface. Too low and the clutch clicks before the screw is fully seated.

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Drive the screw in a single continuous motion. Don't start and stop repeatedly. If the screw resists, back it out and check your pilot hole. Forcing a screw that's binding will either snap the screw (common with cheaper brands) or split the timber.

Impact drivers are better than combi drills for driving screws. They deliver rotational impact pulses rather than continuous torque, which means less cam-out, less wrist strain, and faster driving. If you're driving more than a dozen screws, an impact driver is worth having.

How much do you need

For a single job, count the fixings and add 10% for waste, dropped screws, and the odd one that snaps.

Common quantities for extension work:

• Floorboards to joists - two screws per joist crossing, per board. A 4m x 5m room with joists at 400mm centres has roughly 12 joist crossings per board. With 8 boards across the room, that's about 200 screws. Buy a box of 200 in 5x65mm or 5x75mm.
• Kitchen base units - four screws per unit for the wall rail, two to join each pair of adjacent units, plus legs and plinths. A 10-unit kitchen uses roughly 80 to 100 screws in 4x30mm and 4x40mm.
• Kitchen wall units - two to four heavy screws per unit into wall plugs (5x80mm or 5x100mm), plus internal shelf fixings. Budget 60 to 80 screws for a full kitchen.
• Roof battens - two nails per rafter crossing is standard, but timber noggins, binders, and other connections use screws. Allow a box of 100 in 4.5x60mm or 5x80mm.

A general-purpose trade pack of assorted sizes covers most small to medium jobs without buying five separate boxes. The Screwfix Goldscrew 1,400-piece trade pack contains nine common sizes for around TBC. That works out at roughly 1.4p per screw.

Cost and where to buy

Budget brands

Screwfix Goldscrew and Toolstation's Spectre and Screw-Tite ranges are the budget options. They work fine for softwood interior jobs. Drive quality is acceptable. Cam-out happens occasionally with worn PZ2 bits, but fresh bits solve that.

Mid-range brands

TurboGold (Screwfix) and Timco C2 are the step up. Better drive engagement, underhead ribs that cut a cleaner countersink, and more consistent quality across the box. TurboGold 200 packs are often on "buy 2 for TBC" offers, making them barely more expensive than Goldscrew.

Timco C2 is widely available on Amazon and from trade fixings suppliers. A 200-pack of 4x40mm runs around TBC.

Professional brands

Reisser Cutter and Spax are the ones tradespeople choose when quality matters. Reinforced collars that prevent snapping, split-prevention slots in the thread, deeper PZ recesses that virtually eliminate cam-out, and coatings that tolerate short-term outdoor exposure.

Spax 5x40mm (200 pack) costs around TBC at Screwfix. Spax 5x80mm (100 pack) runs TBC at Toolstation. That's roughly double the budget equivalent.

Are they worth it? If you're driving hundreds of screws into hardwood, joining structural timber, or doing visible joinery where split-free results matter, yes. For fixing battens to a stud wall, Goldscrew will do.

Community consensus across UK forums is consistent: "Screwfix Goldscrew is the best compromise between performance and price. Reisser Cutter is the best screw on the market." Professional fabricators who can pick any brand tend to reach for Reisser.

Stainless steel premium

Expect to pay two to three times the zinc-plated price for A2 stainless equivalents. A box of A2 stainless 4.5x35mm (100 pack) runs around TBC. Non-negotiable for any permanent exterior application.

Where to buy

Screwfix and Toolstation are the go-to sources. Both stock budget through premium ranges, offer click-and-collect within an hour, and have trade counters in most UK towns. Screwfix's Goldscrew and TurboGold ranges are own-brand and represent the best value at their respective tiers.

B&Q and Wickes stock wood screws but the range is smaller and prices tend to be slightly higher than the fixings specialists. Fine if you're already there buying timber.

Amazon is competitive on Timco C2 and Reisser Cutter bulk packs, often undercutting Screwfix on boxes of 200 or more.

Alternatives

Nails are faster to drive (a framing nailer puts in 100 nails in the time it takes to drive 20 screws) and cheaper per unit. But nails have roughly half the withdrawal resistance of screws. They hold against shear forces (sideways loads) almost as well, which is why structural carpenters still nail roof trusses and wall frames. For anything you might need to disassemble, or where pullout resistance matters (floorboards, kitchen units, shelving), screws are the right choice.

Coach bolts are for heavy-duty timber-to-timber connections where a wood screw isn't strong enough. Bolting a ledger board to a wall, connecting large structural timbers, or fixing heavy gate posts. They pass through pre-drilled holes in both pieces and are tightened with a nut and washer from the back. Overkill for anything a 5mm or 6mm screw can handle.

Pocket-hole screws are a specific type of wood screw designed for pocket-hole joinery (jigs that drill an angled hole for a concealed screw joint). These use a square (Robertson) drive, not Pozi. If you're using a Kreg jig or similar, buy the matching screws rather than trying to use standard wood screws.

Where you'll need this

Wood screws turn up across most phases of a building project:

• Roof framing - fixing battens, noggins, and secondary timber connections where nails aren't sufficient or where adjustment might be needed
• Kitchen fitting - securing base units to walls, joining units together, fixing worktops, attaching plinths and cornice. The most screw-intensive single task on most projects
• Flooring - fixing floorboards and sheet materials (plywood, chipboard overlay) to joists. Screws prevent the creaking that nailed floorboards develop over time
• General joinery and trim - skirting boards, architraves, built-in storage, stud wall construction, door lining installation

Common mistakes

Using interior screws outside. The single most reported screw failure in UK DIY forums. Standard yellow zinc-plated screws are for indoor use only. Every box says so, but people don't read boxes. Use A2 stainless for exterior work. Always.

Wrong gauge for the job. A 3.5mm screw holding a kitchen wall unit to the wall is dangerous. Wall units carry the weight of crockery, tins, and appliances. Use 5mm gauge minimum into wall plugs, and check the plugs are rated for the load.

Not pre-drilling near edges. Driving a screw within 20mm of a timber edge without a pilot hole will split the wood. It happens every time in hardwood and most of the time in softwood. The split often runs the full length of the piece. Drill pilot holes near edges and ends without exception.

Overtightening. The clutch on your drill exists for a reason. Driving a screw past flush strips the hole in softwood and chipboard, reducing holding power to almost nothing. In MDF, overtightening blows out the back face. Set the clutch so the screw stops with the head flush to the surface.

Mixing drive types on the same job. Starting with Pozi screws, running out, and finishing with Phillips because "they look the same." They're not the same. A PZ2 bit in a Phillips screw, or a Phillips bit in a Pozi screw, cams out constantly and damages the head. Check what you're driving and use the matching bit.

Buying too short. The screw needs to penetrate the second piece by at least the thickness of the first piece, ideally twice that. A 30mm screw through two 18mm pieces of plywood leaves just 12mm of thread in the bottom piece. That's not enough. Use 40mm or 50mm.

Skipping the clearance hole when joining timber. Without a clearance hole through the top piece, the screw thread grips both pieces simultaneously. The result is a gap between the two that no amount of clamping will close. Drill the clearance hole. It takes ten seconds and makes the joint tight.