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