Guide to Screws and Bolts
There are many different types of screws and bolts available, some for general jobs, and some for very specific DIY tasks. Choosing the correct type for any particular DIY project can make a big difference to its success or failure, but working out exactly which screw or bolt you need can be confusing if you are not used to using them.
This guide aims to introduce you to some of the many different types of screws and bolts available to the DIY-er, from simple Wood Screws, to the more unusual J-Bolts and Hanger Bolts.
Types of Screw
There are many different types of screws available, but many are used for quite specific tasks.
Wood Screws
Screws with a smooth shank and tapered point for use in wood.
Machine Screws
Screws with threads for use with a nut or tapped hole.
Thread-Cutting Machine Screws
Machine screws with a thread cutting (self tapping) point.
Sheet Metal Screws (SMS)
Fully threaded screws with a point for use in sheet metal.
Self-drilling SMS
A Sheet metal screw with a self drilling point.
Socket Screws
Socket screws, also sometimes known as Allen head screws, are fastened with a hex Allen wrench.
Twinfast Screw (Double Spiral Thread)
Screw in very quickly and hold much better than normal threaded screws. Ideal for fixing chipboard, fibreboard and blockboard.
Coach Screws
Generally used in heavier construction. Coach screws are driven into a prepared hole and then tightened with a spanner.
Types of Bolt
Bolts generally (but not always) differ from screws in that they have flat ends, and can be paired with a threaded nut.
Hex Bolts
Bolts with a hexagonal head with threads for use with a nut or tapped hole.
Carriage Bolts
Bolts with a smooth rounded head that has a small square section underneath.
Lag Bolts
Bolts with a wood thread and pointed tip.
Flange Bolts
Flange bolts have a flange on the bottom of the head that distributes the load like a washer.
Eye Bolts
A bolt with a circular ring on the head end. Used for attaching rope or chain.
Eye Lags
Similar to an eye bolt but with wood threads instead of machine thread.
U-Bolts
Bolts in U shape for attaching to pipe or other round surfaces. Also available with a square bend.
J-Bolts
J shaped bolts are used for tie-downs or as an open eye bolt.
Hanger Bolts
Hanger bolts have wood thread on one end and machine thread on the other end.
Types of Screw Head
Countersunk Head
Used for general joinery. Ideal if you need the head to be flush with the material.
Raised Countersunk Head
Normally used in ironmongery or if screw caps are going to be used for a cleaner finish.
Dome Heads
Used for fixing mirrors and plastic sheets or panels. Head can be topped with a decorative dome or plastic clip-on cover.
Roundhead
Generally used for fixing sheet material which is too thin to be countersunk.
Star Head
Require special screwdrivers to tighten and undo. The additional slots improve contact and make it less likely the screwdriver will slip and damage the surface.
Clutch head
Tamper-proof wood screws. These screws have a head designed in such a way that they cannot be easily removed once screwed in.
Types of Drive
Phillips (Cross head)
The standard drive type for most screws.
Frearson
Similar to Phillips. Requires a Frearson driver for installation.
Slotted
A simple slot in the head.
Combination
A combination of slotted and Phillips drives.
Socket or Hex
A hexagonal hole for use with an Allen wrench.
One-way
Installs with a normal slotted driver but can not be removed without special tools.
Square
A simple square hole, requires a special driver. Also known as Robertson drive.
Star
Also known as Torx. A six-pointed star pattern, specifically designed to prevent cam-out and stripped heads.
Types of Washer
