Types of screws
For nails, see Types of nails.
Contents |
[edit] Introduction
A screw is a type of fastener, usually made from metal, that commonly comprises a head at one end, and a point at the other, and a shaft shaped so that it can be turned into another material. The shape of the shaft is characterised by a helical ridge which is known as a ‘male thread’ (where the thread is external) or ‘female thread’ (where the thread is internal). Screws are typically used to hold materials or objects together, or to position objects.
The part of the screw that extends from the underside of the head to the tip is referred to as the ‘shank’ and is either fully or partially threaded. Threaded screws are intended to be driven into material or a pilot hole; partially or non-tapered screws are intended to be driven into a tapped hole.
Tools such as screwdrivers are commonly used to insert screws, and the majority are tightened by clockwise rotation.
[edit] Screws and bolts
The terms ‘screws’ and ‘bolts’ are sometimes used interchangeably, however, in simple terms, a bolt passes through a material and into a nut on the other side to bolt items together, whereas a screw threads directly into a material.
Both screws and bolts are often made of steel, and where resistance is required to weather or corrosion, they may be galvanised, or stainless steel, brass, zinc or titanium may be used.
For more information, see Types of bolts.
[edit] Types of screw
There are many different varieties of screw which are selected based on the particular requirement or the materials involved. Some of the most common types include:
[edit] Wood screw
Typically designed with a partially-unthreaded shank and used to attach pieces of timber together.
[edit] Concrete screw
Stainless or carbon steel and used for fastening materials to concrete.
[edit] Masonry screw
Often have a blue coating and are inserted to a pilot hole in masonry.
[edit] Double-ended (dowel) screw
Have two pointed ends and no head. Often used for making hidden joints between two pieces of timber.
[edit] Drive screw
Smooth, round or mushroom-headed with a reduced diameter shank.
[edit] Drywall screw
Often coated with black phosphate and designed with a bugle head. Used to attach drywall to timber or metal studs.
[edit] Eye bolt
A looped head designed to be used as an attachment point. Also used for attaching wires across building surfaces.
[edit] Decking screw
Longer screws which are used for fastening down deck boards.
[edit] Lag screw/bolt
A heavy-duty fastener.
[edit] Chipboard screw
Often wax-coated and used for fastening down chipboard flooring.
[edit] Mirror screw
Designed with a decorative dome or other cover to conceal the head.
[edit] Twinfast screw
Designed with two threads which enable it to driven twice as fast.
[edit] Security head screw
Designed with a head that is impossible to reverse, making it suitable for security applications.
[edit] Screw heads
Different types of heads include:
- Pan head: Rounded, high outer edge with a large surface area.
- Button/dome head: Cylindrical head with a rounded, dome-like top.
- Round head: Dome-shaped and used mainly for decorative purposes.
- Mushroom head: The dome has a lower profile that is designed to prevent tampering.
- Countersunk/flat head: Conical head with a flat outer face and a tapered inner face.
- Oval/raised head: Countersunk bottom and rounded top, often used decoratively.
- Bugle head: A smooth transition from the shank to the angle of the head.
- Cheese head: A disc with a cylindrical outer edge.
- Fillister head: Cylindrical with a slightly convex top surface.
- Flanged head: Can be any style but has the addition, at the base of the head, of an integrated flange which means it does not require a washer.
[edit] Find out more
[edit] Related articles on Designing Buildings Wiki
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