The Complete Guide to Screws, Bolts, and Fixings — Choosing the Right Fastener for Every Job

Why the Right Fixing Matters

A screw is not just a screw. A wood screw driven into a masonry wall without a wall plug holds nothing. A plasterboard screw driven into plasterboard without an anchor pulls straight through under any meaningful load. A mild steel screw used outdoors rusts within months, staining the surrounding material and eventually failing. The fastener must match the material it is driven into, the load it must carry, and the environment it operates in. Getting this right is straightforward once you understand the basic categories — and this guide gives you exactly that understanding.

Screws — The Workhorse of Home Improvement

Wood screws

Wood screws have a tapered shaft with a coarse, deep thread designed to cut into timber and grip the wood fibres. They are the most commonly used screw in domestic projects — assembling furniture, fixing shelving, attaching hinges, securing timber to timber.

Twin-thread (double-thread) wood screws are the modern standard. The double thread drives the screw into softwood quickly and without the need for a pilot hole in most cases. They are faster to install and provide good holding power.

Single-thread wood screws are the traditional type, requiring a pilot hole and a shank clearance hole for proper installation. They are less commonly used now but remain available for specific applications.

Chipboard screws have a fully threaded shaft (threads run the entire length) and are designed for manufactured boards — chipboard, MDF, plywood, and oriented strand board. Their full thread length provides maximum grip in these materials, which have less holding power than solid timber.

Self-tapping screws

Self-tapping screws cut their own thread as they are driven in, eliminating the need for a pre-tapped hole. They are designed for thin metal, plastic, and some composite materials. The hardened point and aggressive thread cut into the material without splitting it.

Self-drilling screws

Self-drilling screws (also called tek screws) have an integrated drill point that drills its own hole before the thread engages. They are used for fixing into metal — steel framing, metal roofing, and metal-to-metal connections — without a separate pre-drilling step.

Masonry screws

Masonry screws (also called concrete screws) drive directly into masonry, concrete, and brick without the need for a wall plug. They have a hardened steel body and a special thread profile that cuts into the masonry. A pilot hole must be drilled first with a masonry bit, but no plug is inserted — the screw threads grip the masonry directly.

Drywall screws

Drywall screws have a bugle-shaped head that sits flush with the plasterboard surface without tearing the paper face. They are used for fixing plasterboard to timber or metal studs. Their fine thread and sharp point penetrate plasterboard cleanly.

Head Types — Countersunk, Pan, Hex, and More

Countersunk heads are designed to sit flush with or below the surface of the material. They are the standard for woodworking and general fixing where a smooth, flat surface is required.

Pan head screws have a slightly rounded, raised head that sits proud of the surface. They are used with washers or in applications where a flush finish is not required.

Hex head screws and bolts have a six-sided head driven with a spanner or socket. They are used for heavy-duty fixings — coach screws, structural bolts, and mechanical fastenings.

Flange head screws have a built-in washer flange that spreads the clamping load over a wider area, reducing the risk of the head pulling through thin materials.

Round head screws are the traditional raised head type, now largely replaced by pan head screws in modern applications.

Drive Types — Pozidrive, Phillips, Torx, and Hex

The drive type is the shape of the recess in the screw head that the screwdriver or bit engages with.

Pozidrive (PZ) is the most common drive type for wood screws in many markets. It has a cross-shaped recess with additional diagonal markings. It provides better grip and less tendency to cam out (the driver slipping out of the recess) than Phillips.

Phillips (PH) is the traditional cross-head drive. It is common on machine screws and older fasteners. The rounded recess is designed to cam out under excessive torque — this was originally an intentional feature to prevent over-tightening on production lines, but it is a frustration in manual use.

Torx (TX or star drive) has a six-pointed star recess that provides excellent grip with virtually no cam-out. It is increasingly popular for wood screws, decking screws, and any application where high torque is needed without the driver slipping.

Hex (Allen key) drive uses a hexagonal recess. It is common in furniture assembly, machine screws, and set screws.

Slot (flathead) drive is the oldest type — a single straight slot. It is now rarely used for new fixings as it provides poor grip and cams out easily, but it remains on older hardware and some decorative fittings.

Bolts — When Screws Are Not Enough

Bolts differ from screws in that they typically pass through the materials being joined and are secured with a nut on the other side. This provides a stronger, more rigid connection than a screw gripping into material by thread alone.

Coach bolts (carriage bolts) have a smooth, domed head with a square section beneath that locks into timber when tightened, preventing the bolt from spinning. They are used for heavy-duty timber-to-timber connections — decks, fences, gates, and structural frames.

Hex bolts have a hexagonal head and are tightened with a spanner or socket. They are the standard bolt for general mechanical and structural applications.

Expansion bolts (rawl bolts) are heavy-duty masonry anchors. A bolt passes through an expanding sleeve that is inserted into a pre-drilled hole in masonry or concrete. As the nut is tightened, the sleeve expands against the sides of the hole, creating an extremely strong anchor. They are used for fixing heavy items to masonry — wall-mounted television brackets, gate posts, structural steelwork, and heavy shelving.

Threaded rod (studding) is a length of rod threaded along its entire length. It is cut to size and used with nuts and washers at each end to create custom-length through-bolts. Useful for structural connections, securing posts, and creating fixings where standard bolt lengths are not available.

Nails — The Fastest Fastener

Nails are driven into material with a hammer rather than rotated with a screwdriver. They are faster to install than screws but provide less holding power and are more difficult to remove without damaging the material.

Round wire nails are general-purpose nails for rough carpentry — fixing framing timber, temporary constructions, and non-finish work. They can split timber if driven too close to the edge.

Oval wire nails have an oval cross-section that is less likely to split timber. They are used for joinery and finish carpentry where splitting must be avoided.

Lost-head nails (panel pins) are small, thin nails with a minimal head that can be punched below the surface and filled. They are used for fixing mouldings, trim, and beading.

Masonry nails are hardened steel nails driven directly into masonry and concrete with a heavy hammer. They are used for fixing timber battens and small items to masonry where a wall plug and screw would be unnecessarily time-consuming.

Ring shank nails have annular rings along the shaft that greatly increase resistance to withdrawal. They are used where holding power is critical and removal is not expected — flooring, sheathing, and permanent structural connections.

Wall Plugs — Making Screws Work in Masonry

A screw driven directly into masonry (brick, block, stone, concrete) has almost no holding power — the screw threads cannot grip the hard material. A wall plug solves this problem by providing a soft, expandable sleeve within the masonry that the screw threads can grip.

The principle: Drill a hole in the masonry with a masonry drill bit. Insert the wall plug (a tapered plastic or nylon tube). Drive the screw into the plug. As the screw enters, the plug expands against the sides of the hole, gripping the masonry and locking the screw in place.

Colour-coded sizing

Wall plugs are colour-coded by size across most manufacturers.

Yellow plugs are the smallest — for screw gauges 4 to 8, drilled with a 5 mm masonry bit. Suitable for lightweight fixings — small shelving, light fittings, hooks, and decorative items.

Red plugs are medium — for screw gauges 6 to 10, drilled with a 6 mm masonry bit. Suitable for medium-weight fixings — curtain poles, towel rails, wall-mounted cabinets, and general household fixings.

Brown plugs are large — for screw gauges 10 to 14, drilled with a 7 mm masonry bit. Suitable for heavy fixings — large shelving, wall-mounted televisions (on solid masonry), boilers, and heavy hardware.

The screw length must be long enough to pass through the item being fixed and penetrate at least three-quarters of the plug length into the wall. A screw that is too short does not fully expand the plug and provides reduced holding power.

Plasterboard Fixings — The Hollow Wall Challenge

Plasterboard (drywall) is a thin, relatively weak panel. A standard wall plug and screw simply pushes through it under load — there is not enough material for the plug to grip. Plasterboard fixings work by spreading the load across a wider area of the plasterboard or by gripping the back face of the board.

Self-drilling plasterboard anchors screw directly into the plasterboard, creating their own hole. Plastic versions are suitable for light loads. Metal versions hold more weight.

Spring toggle fixings pass through a hole in the plasterboard and spring open behind it, spreading the load across a wide area of the board's back face. They are suitable for medium to heavy loads on hollow walls.

Metal cavity wall anchors (hollow wall anchors) are inserted through a hole in the plasterboard. As the screw is tightened, the anchor collapses and clamps against the back of the board, providing a strong mechanical grip. They are the strongest plasterboard fixing available for most domestic applications.

The strongest approach for heavy items on plasterboard walls is to locate the timber studs behind the board (using a stud finder) and screw directly into the studs. This provides full timber-screw holding power rather than relying on the plasterboard itself.

Materials and Coatings — Steel, Stainless, Brass, and Zinc

Mild steel (with zinc plating or passivation) is the standard material for indoor screws and fixings. The zinc coating provides moderate corrosion resistance for dry interior environments.

Stainless steel provides excellent corrosion resistance and is essential for outdoor use, wet environments (bathrooms, kitchens), and coastal locations where salt air accelerates corrosion. A2 grade stainless steel is suitable for most outdoor applications. A4 grade provides additional corrosion resistance for marine and coastal environments.

Brass screws are used for decorative applications and traditional hardware where the warm, golden colour of brass is desired. Brass is softer than steel — brass screws can strip or break more easily than steel equivalents, so pilot holes are always advisable.

Zinc-plated (BZP — bright zinc plated) screws are standard mild steel with a thin zinc coating. Suitable for indoor use. Not recommended for prolonged outdoor exposure as the zinc layer is relatively thin.

Yellow zinc plated (YZP) provides additional corrosion resistance over standard BZP, with a gold-coloured finish. Sometimes preferred for appearance.

Hot-dip galvanised screws have a thick zinc coating applied by dipping in molten zinc. They provide the best zinc-based corrosion resistance for outdoor use where stainless steel is not required.

Sizing — Understanding Length, Gauge, and Metric Designations

Traditional gauge system: Wood screws were historically sized by gauge number (a legacy measurement of shaft thickness) and length in inches or millimetres. A No. 8 × 40 mm screw has a gauge 8 shaft and is 40 mm long.

Metric system: Modern screws are increasingly designated by shaft diameter and length in millimetres. A 4 × 40 mm screw has a 4 mm shaft diameter and is 40 mm long.

Bolt sizing uses the metric designation M followed by the shaft diameter. An M6 × 50 bolt has a 6 mm diameter shaft and is 50 mm long.

Length is measured from the point that sits flush with the surface. For countersunk screws, the length includes the head. For pan head and hex head screws, the length is measured from under the head.

Fastener Comparison Table

Common Mistakes People Make

Using a wall plug that is too small for the load

A yellow wall plug holding a heavy shelf bracket is an accident waiting for enough time to pass. Match the plug size to the load — heavier items need larger plugs with correspondingly larger screws.

Drilling into plasterboard and assuming it is solid wall

Many homeowners drill into a wall, insert a standard wall plug, and wonder why the screw spins freely and holds nothing. If the drill bit pushes through into a void after 12 to 15 mm, you have a plasterboard wall and need a plasterboard-specific fixing.

Using indoor screws outdoors

Standard zinc-plated screws rust rapidly in outdoor exposure. Within months, the screws rust, stain the surrounding timber, and lose structural integrity. Use stainless steel or hot-dip galvanised screws for all outdoor fixings.

Not drilling a pilot hole in hardwood

Hardwood resists screw penetration. Driving a screw into hardwood without a pilot hole risks splitting the timber, snapping the screw, or stripping the drive recess. Always drill a pilot hole slightly smaller than the screw core diameter.

Over-tightening screws in plasterboard

A screw tightened too far in plasterboard crushes through the paper face, destroying the board's holding capacity at that point. Stop tightening when the screw head sits just flush with the surface.

Using the wrong drive bit

A Phillips bit in a Pozidrive screw (or vice versa) feels similar but does not engage properly. The result is cam-out, a damaged screw head, and frustration. Check the screw drive marking and use the corresponding bit.

The Honest Limitations

No screw is stronger than the material it is driven into. A large screw in weak material holds less than a small screw in strong material. The strength of the fixing is always limited by the weakest component — whether that is the screw, the plug, or the wall material.

Plasterboard has inherent weight limits. Even the best plasterboard fixings have load limits that are a fraction of what a masonry or timber fixing can hold. For genuinely heavy items on plasterboard walls, finding and fixing into the studs is always the most reliable approach.

Screws do not replace structural engineering. Load-bearing connections in building structures — roof trusses, floor joists, structural beams — require fixings that are specified by an engineer or building designer. DIY-selected screws and bolts are appropriate for domestic projects, not structural connections.

Corrosion is progressive. A screw that shows surface rust today will be significantly weaker next year. Outdoor fixings should be inspected periodically and replaced when corrosion is visible.

Pre-Purchase Checklist

What material are you fixing into?

Timber: wood screws. Masonry (brick, concrete, block): masonry screws or wall plugs with screws. Plasterboard: plasterboard-specific fixings. Metal: self-tapping or self-drilling screws.

How heavy is the item being fixed?

Light (pictures, small shelves): small wall plugs or plasterboard anchors. Medium (curtain poles, cabinets): medium wall plugs or metal cavity anchors. Heavy (television brackets, boilers): large wall plugs, expansion bolts, or stud fixing.

Is the installation indoors or outdoors?

Indoor: standard zinc-plated screws. Outdoor: stainless steel or hot-dip galvanised.

Do you need the screw to be invisible?

If yes: countersunk head, driven flush or below the surface and filled. If not: pan head or hex head for easy identification and removal.

Do you have the right drill bits?

Masonry fixing requires a masonry drill bit. Timber fixing may require a pilot drill bit in hardwood. Plasterboard anchors may require a specific hole size.

Why Buying Through Amazon Is a Smart Option

Amazon carries the full range of screws, bolts, nails, wall plugs, and specialist fixings from all major manufacturers — in every size, material, and head type. Assorted packs provide a selection of sizes for a single project or a general-purpose toolkit. Customer feedback provides practical insight into holding strength, corrosion resistance, and real-world performance. Free returns on most purchases allow you to exchange a wrong size without a wasted trip.