Nuts, bolts and washers look simple, but picking the wrong one costs you a return trip to the merchant or a joint that works loose. This guide runs through the common types of nuts and bolts, the washers that go with them, how sizes are measured, and how to choose the right fixing for the job. Everything here is stocked as genuine TIMCO, so you can jump straight to the range when you know what you need.

Bolts: the main types and what they are for

A bolt is a threaded fixing used with a nut (or tapped into a threaded hole). The head shape is what usually tells you the type.

• Carriage bolts have a domed head and a square shoulder under it that bites into timber so the bolt cannot spin while you tighten the nut. They are the go-to for clamping timber and fixing ironmongery to wood. See our carriage bolts.
• Coach bolts is the traditional name for the same domed, square-shouldered bolt, so the two terms are used interchangeably in the UK.
• Set screws and hex bolts have a six-sided head for a spanner or socket. A set screw is fully threaded; a bolt in the strict sense has a plain shank under the head. Grade 8.8 set screws (to DIN 933) suit structural and machinery work.
• Roofing bolts have a low mushroom head and come with a square nut, made for fixing sheet and cladding.
• Machine screws are small bolts with a slotted or pozi head, used with a nut for light panel and electrical work.
• Masonry bolts such as throughbolts and shield anchors fix into concrete and brick without timber, expanding to grip the hole.

Bolt head types at a glance

The four heads you will meet most often are the domed carriage head, the hex head, the low roofing (mushroom) head, and the countersunk head that sits flush. Match the head to the look and the tool you have: hex for a spanner, pozi or slot for a screwdriver, carriage for timber.

Nuts: holding it all together

• Hex full nuts (DIN 934) are the standard nut for general bolting. Browse hex nuts.
• Nyloc (nylon insert) nuts have a nylon collar that grips the thread and resists shaking loose, so they suit anything that vibrates. See our nyloc nuts.
• Square nuts pair with roofing bolts and channel systems, where the flat sides help them sit still.
• Channel nuts lock into strut and support channel for pipework and services.

Washers: why they matter

A washer spreads the clamping load, protects the surface, and helps stop the fixing pulling through or working loose. Skip it and a nut can bite into timber or crush a soft material.

• Form A flat washers (DIN 125A) are the general-purpose choice under most nuts and bolt heads. See Form A washers.
• Penny (repair) washers have a large outside diameter for spreading load on soft or thin material and covering oversized holes. See penny washers.
• Square plate washers spread load across timber in structural connections.
• EPDM and dowty sealing washers add a bonded rubber face to keep water out on roofing and pipework. Browse all washers.

How nuts and bolts are measured

Metric bolts are described as diameter by length, for example M10 x 100. The M number is the thread diameter in millimetres, and the length is measured under the head (except countersunk heads, which are measured overall). Nuts and washers are sized to the same M number, so an M10 bolt takes an M10 nut and an M10 washer.

This table covers the common metric coarse sizes and the spanner you need:

Finishes and where to use them

The finish decides how long a fixing lasts outdoors. As a rough guide:

• Zinc plated (BZP) suits clean, dry indoor use.
• Hot-dip galvanised (HDG) stands up to outdoor and damp conditions.
• Exterior coated (green) carriage bolts are made for external timber such as decking and fencing.
• Stainless steel (A2) gives the best corrosion resistance for coastal or wet work.

TIMCO grade its fixings by corrosion rating, so check the rating on the product page if the fixing will live outside.

How to choose and put it together

Work through it in order. Pick the bolt type for the job (carriage for timber, hex set screw for steel, masonry bolt for concrete). Choose the diameter and length: the bolt should pass fully through the joint with a couple of threads showing past the nut. Add a washer under the nut, and a second under the head on soft material. Then match the finish to the environment. If you keep a mix of sizes on the van, a nuts, bolts and washers tray saves the trip to the merchant.

For door, gate and cabinet hardware to finish the job, see our ironmongery range, and for the full picture start at the fixings and fasteners hub.

Frequently asked questions

What are nuts and bolts?

A bolt is a threaded metal fixing with a head at one end. A nut is the threaded collar that screws onto it. Tightening the nut clamps whatever sits between the head and the nut, usually with a washer to spread the load.

Which is the nut and which is the bolt?

The bolt is the long threaded part with the head. The nut is the small six-sided (or square) piece that screws onto the end.

How do I measure a nut and bolt?

Measure the thread diameter across the threads and the length under the head. A bolt marked M10 x 100 has a 10mm thread and is 100mm long. The nut and washer use the same M number.

Why do nuts and bolts need washers?

A washer spreads the clamping force over a wider area, protects the surface from the turning nut, and helps keep the joint tight. On soft or thin materials it stops the fixing pulling through.

What is a nyloc nut?

A nyloc nut has a nylon insert that grips the bolt thread, so it resists loosening from vibration. It is the nut to reach for on machinery, trailers and anything that shakes.

What is a penny washer?

A penny (or repair) washer has a large outside diameter compared with its hole, so it spreads load over a big area and covers oversized or worn holes.

How do I loosen a rusted nut and bolt?

Give it a soak with penetrating oil and leave it, tap the nut to shock the rust, then try again with a well-fitting spanner or socket. Heat can help on stubborn joints, and a nut splitter is the last resort.

What is the difference between a carriage bolt and a coach bolt?

They are the same fixing. Both have a domed head and a square anti-spin shoulder for timber. Coach bolt is the older UK name, carriage bolt the more common one today.

Every nut, bolt and washer mentioned here is stocked as genuine TIMCO and supplied by Stick2 Products at UK trade prices. Browse bolts, nuts and washers, or the full fixings and fasteners range.