Types of Screws
- Cap screw has a convex head, usually hexagonal, designed to be driven by a spanner or wrench.
- Wood screw has a tapered shaft allowing it to penetrate undrilled wood.
- Machine screw has a cylindrical shaft and fits into a nut or a tapped hole, a small bolt.
- Self-tapping screw has a cylindrical shaft and a sharp thread that cuts its own hole, often used in sheet metal or plastic.
- Drywall screw is a specialized self-tapping screw with a cylindrical shaft that has proved to have uses far beyond its original application.
- Set screw has no head, and is designed to be inserted flush with or below the surface of the workpiece.
- Double-ended screw is a wood-screw with two pointed ends and no head, used for making hidden joints between two pieces of wood.
Shapes of Screw Head
- Pan head: disc with chamfered outer edge.
- Cheese head: disc with cylindrical outer edge.
- Countersunk: conical, with flat outer face and tapering inner face allowing it to sink into the material, very common for wood screws.
- Button or dome head: flat inner face and hemispherical outer face.
- Mirror screw head: countersunk head with a tapped hole to receive a separate screw-in chrome-plated cover, used for attaching mirrors.
Types of Screw Drive
A variety of tools exist to drive screws into the material to be fixed. The hand-tool used to drive slot-headed and cross-headed screws is called a screwdriver. A power tool that does the same job is a power screwdriver. The hand-tool for driving cap screws and other types is called a spanner (UK usage) or wrench (US usage).
- Slot head is driven by a flat-bladed screwdriver.
- Cross-head, or Phillips screw has an X-shaped slot and is driven by a cross-head screwdriver, designed originally in the 1930s for use with mechanical screwing machines, intentionally made so the driver will ride out, or cam out, under strain to prevent over-tightening.
- Pozidriv is patented, similar to cross-head but with better resistance to slipping, or cam-out.
- Hexagonal or hex screw head has a hexagonal hole and is driven by a hexagonal wrench, sometimes called an Allen key, or a power tool with a hexagonal bit.
- Robertson drive head has a square hole and is driven by a special power-tool bit or screwdriver (this is a low-cost version of the hex head for domestic use).
- Torx head has a splined socket and receives a driver with a splined shaft.
- Tamper-proof torx is similar to torx but the drive socket has a projection to prevent a standard torx driver being inserted.
- Tri-Wing screws are used by Nintendo on its Gameboys. This discourages even minor home repairs to the units.
Nuts are square, round, or hexagonal metal blocks with a screw thread on the inside. Nuts help fasten objects together and are used with screws or bolts. This page uses material from the Wikipedia article "Screw" licensed under the GNU Free Documentation License.