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Wood screws are designed for solid-wood and timber joints, with a tapered shank, coarse thread, and sharp point that grip wood fibres for strong withdrawal resistance. DIN 95 (oval countersunk), DIN 96 (round), and DIN 97 (flat countersunk) define the standard head styles. Sizes span imperial #2–#14 and metric equivalents. Carbon steel zinc-plated for interior work; A2/A4 stainless and HDG for outdoor and treated-lumber applications.
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A wood screw is a threaded fastener for solid timber: the shank tapers from tip to head, the thread is coarse and deep, and a smooth unthreaded section below the head draws the top piece tight against the bottom piece. The tip is sharp—a gimlet point in traditional screws, a Type 17 auger point in modern production variants.
The tapered shank is what makes it a wood screw. Unlike a machine screw with a constant-diameter body, the wood screw thickens toward the head, matching the natural taper of a properly drilled pilot hole. Full-length thread engagement from tip to root along the entire embedment depth—no wasted thread, no gap at the bottom of the hole.
The screw enters a pilot hole in the lower piece, smaller than the shank at its tip and tapered to match at the head. As the thread bites, the shank wedges into the hole, compressing wood fibers against the thread flanks.
The smooth unthreaded shank spins freely in the upper piece, letting the screw head pull both pieces together without the thread gripping the top board. A fully threaded wood screw cannot close a joint because the threads lock into the top board and stop it from sliding down toward the joint line. Partially threaded screws solve this.
| Style | Profile | Application |
|---|---|---|
| Flat Countersunk | Tapered underside at 82° (standard in North America) or 90° (DIN 97, European) | Flush with the wood surface; fillable with putty or plug for invisible fastening |
| Oval Countersunk | Countersunk underside with a domed top | Visible hardware in fine furniture—the dome stands proud as a design detail |
| Round Head | Full domed head, flat bearing surface | Mounting brackets, hardware, and thin metal to wood where countersinking isn’t needed |
| Pan Head | Low dome with flat underside | General assembly; shallower head height than round |
| Trim / Finishing Head | Small-diameter flat head, sinks below surface | Finish carpentry and trim work; the small head is easy to cover with filler |
| Washer / Flange Head | Countersunk with integral flat washer face | Spreading clamp load on softwoods that crush under standard head bearing pressure |
| Drive | Notes |
|---|---|
| Slotted | Traditional. Dominated wood screws for a century. Cam-out is inherent—the driver walks out of the slot under torque. Still specified for restoration work matching period hardware. |
| Phillips (PH) | Engineered to cam-out at a controlled torque. PH2 is standard for #6–#10 screws. Slippage under high torque in hardwood—keep the driver perfectly square to the screw. |
| Pozi (PZ) | Phillips-compatible visually but not functionally—the extra ribs between the cruciform arms grip better. PZ2 is standard for #8–#12 screws. An upgrade over Phillips for the same bit cost. |
| Square (Robertson) | Standard in Canada, growing in the US. The square recess holds the screw on the bit without a magnetic tip. SQ2 covers most #6–#10 wood screws. Cam-out is eliminated: the driver slips before the recess strips. |
| Torx / Star (T) | Maximum torque transfer. No cam-out. T15–T25 cover most wood screws. The standard for production and impact drivers. The bit and screw are a matched system—a worn Torx bit strips screws faster than a worn Phillips bit strips Phillips screws. |
Square and Torx are the modern defaults for production woodworking. Slotted remains in restoration and reproduction work where period-correct fasteners matter more than assembly efficiency.
Standard Wood Screw Partially threaded, tapered shank, gimlet point. The baseline. For general joinery where the joint is clamped before screwing and the screw delivers clamping force and withdrawal resistance. Sizes #2 to #24, lengths 1/4 in. to 6 in.
Deck Screw A wood screw optimized for outdoor decking boards. Type 17 auger point self-drills through deck boards without a pilot hole. Fully threaded for maximum grip in pressure-treated lumber. Coating is either ACQ-compatible polymer (for modern pressure-treated wood, which is corrosive to standard zinc) or 305/316 stainless. Bugle head reduces mushrooming around the screw head in soft decking lumber. Common sizes: #8 × 2-1/2 in., #10 × 3 in.
Production / Cabinet Screw Fully threaded with a narrow core. Washer head or flat head with ribs for self-countersinking. Engineered for cabinet assembly lines—no pilot hole, no countersink, driven with a clutch-set drill. Often has a wax or polymer coating for reduced driving torque. Overlaps with chipboard screw territory but the thread geometry is tuned for solid wood joinery rather than engineered panels.
Lag Screw / Lag Bolt A heavy-duty wood screw with a hex head, driven by wrench or socket rather than screwdriver. Diameters 1/4 in. to 1-1/4 in., lengths to 12 in. or more. Used for structural timber connections—beams to posts, ledger boards to walls, heavy hinges. Requires a pilot hole. The thread cuts into the wood with a coarse pitch; the hex head delivers torque far beyond what a screwdriver head can handle.
Brass Wood Screw Solid brass, not brass-plated steel. Non-magnetic, corrosion-resistant, decorative. Standard in fine furniture, marine joinery below deck, and architectural millwork. The material is soft—brass threads strip at roughly half the torque of a steel screw. Always drill a pilot hole and lubricate the threads with wax or soap before driving.
Steel (Zinc-Plated) The default. Indoor woodworking where moisture is not a concern. Electroplated zinc at 5–8 µm offers indoor atmospheric protection. Not rated for outdoor use or pressure-treated wood contact.
Steel (Black Oxide / Black Phosphate) Dark matte finish, zero meaningful corrosion resistance. The appeal is aesthetic—black screws on dark woods and painted black hardware are invisible without filling. Oil the threads before driving to prevent the finish from galling in the hole.
Steel (Hot-Dip Galvanized) For outdoor structural timber—deck framing, pergolas, fence rails. Coating thickness 45–55 µm. The coating roughness increases driving torque. Matches well with pressure-treated lumber rated to UC4A ground contact. Not decorative—the finish is rough, matte gray, with drips and high spots.
Stainless Steel 305 / 316 The premium outdoor option. 305 stainless (lower nickel, higher work-hardening) for general deck and fence use. 316 stainless for coastal saltwater exposure and boatbuilding. Stainless wood screws cost roughly 3–4× the galvanized equivalent. For deck boards within 5 km of saltwater, 316 is the minimum that avoids rust staining within a year. 305 may show tea-staining at screw heads within 6–12 months in the same environment.
Solid Brass Decorative and marine. Brass wood screws in traditional slotted flat-head are the standard for period furniture reproduction. Pre-drilling is mandatory—brass is too soft to overcome the friction of an unthreaded pilot hole. Lubricate every screw with wax. A snapped brass screw buried below the wood surface is a problem: the soft metal resists extraction with a screw extractor.
Silicon Bronze Marine wood screws for boatbuilding, docks, and saltwater piers. Silicon bronze is stronger than brass, roughly matching mild steel in tensile strength, and utterly immune to saltwater corrosion. Cost is roughly 5–6× galvanized steel. Used where a broken fastener would require structural disassembly of a hull or dock section.
Wood screws use gauge numbers in imperial sizing, not fractional inches. The gauge is a historical wire-gauge system—the number does not correspond to any simple fraction of an inch.
| Gauge (#) | Nominal Diameter (in.) | Nominal Diameter (mm) | Common Lengths (in.) | Typical Use |
|---|---|---|---|---|
| 2 | 0.086 | 2.2 | 1/4–3/4 | Craft, small hardware, hinges on jewelry boxes |
| 4 | 0.112 | 2.8 | 3/8–1-1/2 | Light-duty hardware, drawer pulls, small brackets |
| 6 | 0.138 | 3.5 | 1/2–2 | Cabinet assembly, face frames, hinges on cabinetry |
| 8 | 0.164 | 4.2 | 5/8–3 | General joinery, door hinges, medium brackets |
| 10 | 0.190 | 4.8 | 3/4–4 | Structural assembly, stair treads, heavy hinges |
| 12 | 0.216 | 5.5 | 1– | Timber framing, heavy furniture, ledger connections |
| 14 | 0.242 | 6.1 | 1-1/4– | Heavy timber, beam-to-post connections |
Metric wood screws follow ISO/DIN sizing: M2, M2.5, M3, M3.5, M4, M5, M6, M8, M10.
Length selection: The threaded portion should penetrate at least half the thickness of the lower piece, and the smooth shank length should equal the thickness of the upper piece. For a 3/4 in. board screwed to a 1-1/2 in. post: a #10 × 2 in. screw with roughly 3/4 in. of smooth shank and 1-1/4 in. of thread.
Hardwood and softwood demand different pilot hole strategies. Hardwood (oak, maple, ash, hickory) resists thread penetration and splits if the hole is undersized. Softwood (pine, fir, cedar, spruce) compresses around the thread and tolerates a tighter hole.
| Screw Gauge | Softwood Pilot (in.) | Hardwood Pilot (in.) | Softwood Clearance (in.) | Hardwood Clearance (in.) |
|---|---|---|---|---|
| #6 | 3/32 | 7/64 | 9/64 | 5/32 |
| #8 | 7/64 | 1/8 | 5/32 | 11/64 |
| #10 | 1/8 | 9/64 | 3/16 | 13/64 |
| #12 | 9/64 | 5/32 | 7/32 | 15/64 |
The pilot hole is the hole in the lower piece—it receives the threaded portion. The clearance hole is the hole in the upper piece—it passes the smooth shank. Without a clearance hole, the screw thread grips the upper piece and holds it away from the joint, leaving a gap.
Furniture Making Hardwood joinery uses #6 to #12 flat-head wood screws with a pilot hole and countersink for every screw. Screws reinforce mortise-and-tenon and dowel joints; they are not the primary connection but the backup. A dining chair with glued dowels in the leg-to-rail joint plus a single #10 screw through the inside corner will survive decades of lateral racking that a dowel-only joint might not.
Decking and Outdoor Structures Deck screws in #8 and #10 with ACQ-compatible coating are the standard for face-screwing deck boards to joists. The Type 17 point eliminates the pilot hole through 5/4 deck boards. For structural framing (joists to beams, posts to footings), lag screws or structural screws with hex heads replace nails—screws resist withdrawal as wood shrinks and swells through seasonal humidity cycles.
Finish Carpentry and Trim Trim-head screws with a small-diameter flat head sink below the surface of baseboards, crown molding, and door casing. The screw holds the trim tight to the wall while construction adhesive cures. The small hole fills with a dab of caulk or spackle—no visible fastener head on painted trim.
Boatbuilding and Marine Joinery Silicon bronze wood screws in flat-head, oval-head, and round-head are the standard for wooden boat construction, dock hardware, and saltwater pier decking. Every screw hole is pre-drilled and countersunk. The bronze screw head is left exposed or bunged with a matching wooden plug—either way, the fastener must survive decades of saltwater immersion and splash. 316 stainless is an alternative; galvanized steel is unacceptable below deck or within the splash zone.
| Decision | What to Ask | Guidance |
|---|---|---|
| 1. Material | Indoor or outdoor? Wood or pressure-treated? | Indoor dry → zinc-plated steel. Indoor aesthetic → brass. Outdoor general → hot-dip galvanized or 305 stainless. Pressure-treated → ACQ-compatible polymer or stainless. Saltwater → 316 stainless or silicon bronze. |
| 2. Head style | Visible or hidden? | Hidden → flat countersunk, filled with putty or plug. Visible decorative → oval or round head. Deck boards → bugle or trim head to reduce mushrooming. |
| 3. Thread type | Single piece or two pieces? | Two pieces being joined → partially threaded with smooth shank. Attaching to a single surface → fully threaded (deck screws, trim screws). |
| 4. Drive | Hand driving or production? | Hand or restoration → slotted or Phillips. Production line → square or Torx. Impact driver → Torx only (square strips under impact). |
| 5. Gauge and length | Joint geometry? | Gauge matches the load—use #8 for cabinet hinges, #12 for stair treads. Length: smooth shank = upper piece thickness, thread ≥ half the lower piece thickness. |
What is the difference between a wood screw and a drywall screw? A wood screw has a tapered shank, coarse deep thread, and smooth upper shank. A drywall screw has a constant-diameter shank, fine thread, bugle head, and phosphate coating. A drywall screw in wood snaps under bending loads that a wood screw tolerates—the drywall screw is case-hardened and brittle.
Do wood screws require a pilot hole? In hardwood—yes, always. The screw will split oak or maple without a pilot hole. In softwood with modern Type 17 auger-point screws—no pilot needed for #8 and smaller. For any screw larger than #10, drill a pilot hole regardless of wood species.
Can I use deck screws for indoor furniture? Functionally yes, aesthetically no. Deck screws have a brown, green, or gray coating that looks industrial on furniture. The thread geometry and holding power are fine—the appearance is the problem. Use standard wood screws for visible fasteners in furniture.
What is a Type 17 point? A cutting notch at the screw tip that drills an entry hole and clears chips during driving. It eliminates the pilot hole in softwood and reduces splitting in hardwood. Standard on deck screws and modern production wood screws.
Why do brass wood screws break so easily? Brass tensile strength is roughly half that of steel, and it lacks steel’s ductility. The head shears at the thread start if the pilot hole is undersized or unlubricated. Drill the correct pilot hole and wax the threads before driving.
How deep should a wood screw go?