How big should the clearance hole be?

About 1 mm over the bolt diameter. For an M10 bolt, a 10.5-11 mm hole leaves assembly tolerance and keeps the thread off the plate.

Why do bolts come loose?

Vibration and insufficient preload. Tightening to the right torque and, where needed, adding a spring washer or lock nut prevents it.

Which spanner size do I need?

It follows the thread: 10 mm for M6, 13 for M8, 17 for M10 and 19 for M12 are the usual sizes.

Can plated bolts be used outdoors?

In sheltered, short-term use yes, but anywhere that gets wet calls for hot-dip galvanised or stainless (A2/A4).

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Nuts & Bolts

Nuts and bolts are the standard for a metal joint that has to come apart again. This page explains how to read a metric size, how bolt and nut pair up, and what is done about loosening. The catalogue holds 40 plated sizes from M5 to M27.

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Reading a metric size

In M10x50, M10 is the thread diameter (10 mm) and 50 is the length in millimetres from under the head to the tip. The nut matches the same metric size: an M10 bolt takes an M10 nut. The spanner size is the distance across the flats of the head and follows the thread diameter — an M10 bolt is typically tightened with a 17 mm spanner.

The clearance hole is drilled about 1 mm over the bolt diameter, so the thread bears on the nut rather than the plate and some assembly tolerance remains.

Size	Clearance hole	Typical spanner
M6	6.5 mm	10
M8	8.5 mm	13
M10	10.5 mm	17
M12	13 mm	19
M16	17 mm	24

Tightening and stopping it coming loose

A bolted joint holds by tension, not friction: a correctly tightened bolt stretches like a spring and clamps the parts together. Over-tightening strips the thread; under-tightening lets the joint shake loose.

On joints that vibrate, use a washer, a spring washer or a lock nut. Zinc-plated bolts are for indoor and general assembly; anywhere that gets wet calls for hot-dip galvanised or stainless.

Frequently Asked Questions

What does M10x50 mean?
M10 is the thread diameter (10 mm) and 50 the length in millimetres from under the head to the tip. The nut matches the same metric size.
How big should the clearance hole be?
About 1 mm over the bolt diameter. For an M10 bolt, a 10.5-11 mm hole leaves assembly tolerance and keeps the thread off the plate.
Why do bolts come loose?
Vibration and insufficient preload. Tightening to the right torque and, where needed, adding a spring washer or lock nut prevents it.
Which spanner size do I need?
It follows the thread: 10 mm for M6, 13 for M8, 17 for M10 and 19 for M12 are the usual sizes.
Can plated bolts be used outdoors?
In sheltered, short-term use yes, but anywhere that gets wet calls for hot-dip galvanised or stainless (A2/A4).