Question 1

1. What are the standard nut and bolt sizes used for UK building projects?

Accepted Answer

UK construction uses metric dimensions, indicated by an ‘M’ followed by a number (e.g. M8, M12). The “M” stands for metric, and the number refers to the nominal outer diameter of the bolt in millimetres (mm).

For example, an M10 bolt has a 10mm thread diameter. M6 to M10 are common for timber and light fixings, while M12 to M20 are typically used in structural steel and concrete work. Matching nuts will have the same M-size and thread pitch as their bolts.

Question 2

2. What are the most common types of nuts, bolts and washers used in UK construction?

Accepted Answer

Hex bolts, coach bolts, nyloc nuts and plain washers are most frequently used across joinery, steelwork and structural jobs.

Question 3

3. When should I use stainless-steel nuts and bolts?

Accepted Answer

Use stainless-steel nuts and bolts in situations exposed to moisture, chemicals or outdoor conditions to make sure of long-term corrosion resistance.

Question 4

4. How do I know which size of bolt or washer I need?

Accepted Answer

Refer to your building spec or the material load needs of the situation. M6 to M12 is common for timber and light steel; larger sizes suit heavier structural joints.

Nuts, bolts and washers

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