Send us these four measurements and we can identify almost any bolt or screw.
1. Diameter
Measure across the threads with a vernier caliper. A reading near 8 mm is an M8, near 10 mm is an M10. Inch bolts read in fractions, such as 3/8 in (9.5 mm) or 1/2 in (12.7 mm).
2. Thread pitch
Pitch is the distance between two thread crests. Use a thread gauge if you have one, or measure ten threads with the caliper and divide by ten. Metric coarse pitches are standard: M8 is 1.25 mm, M10 is 1.5 mm and M12 is 1.75 mm. Our size finder lists the coarse pitch for each size.
3. Length
Measure from under the head to the tip for hex bolts and cap screws. For countersunk screws, measure the full length including the head. Do not include the head on any other type.
4. Head type and drive
- Hex head: turned with a spanner. Note the spanner size across flats.
- Socket cap head: turned with a hex key. Note the key size.
- Countersunk, button or set screw: also hex key driven, but the head shape differs.
Use the spanner lookup to turn a spanner or key size into a thread size.
Grade
Look for the number stamped on the head, such as 8.8 or 10.9. If nothing is stamped, assume a low grade and tell us the job so we can recommend one. See how to read bolt grades.
Send it to us
WhatsApp a photo of the bolt beside a ruler with the measurements above, and we will confirm the match and quote.