Stover nut sizes.

Stover, and what a K-nut is not

A Stover, or all-metal lock nut, does the same job as a nyloc with no plastic in it — the top of the nut is squeezed out of round so the thread grips. Because there is no nylon to soften, it holds hotter: the standard describes all-metal nuts in service to 150°C against 120°C for a nyloc. You will see 450°F and even 1400°F quoted around the trade; the first is a figure withdrawn from the standard in 2008 and the second is not credible for a carbon steel nut.

One thing to watch if you buy motorsport parts: a "K-nut" is not a Stover, even though it locks the same way. The aerospace-derived ones are a smaller hex on the same thread — an M8 K-nut takes a 10mm spanner where an M8 Stover takes 13mm — so they are a separate line here, deliberately kept off this chart. Confusingly, "K-nut" also gets used for a KEPS nut, which is a nut with a captive washer and a different thing again.

Which class of nut for which bolt

A nut is not graded like a bolt. It carries a single number — its proof load class — and the rule is simple: the nut class is the digit to the left of the bolt class. A class 8 nut for an 8.8 bolt, class 10 for a 10.9, class 12 for a 12.9. Put a class 6 nut on a 10.9 bolt and the nut strips before the bolt reaches its rating, which is exactly the failure you do not want.

Stainless works differently again. On a stainless bolt the number is a tenth of the tensile strength, so A4-80 means 800 MPa. On a stainless nut it is a tenth of the proof load, and the standard's partner for an A4-80 bolt is an A4-70 nut — A4-80 is not a nut designation at all, however often you hear it asked for.

Not sure which you need?

Bring the old one in, or send us a photo. We are on Baird Close in Daventry with metric and imperial stock across the common classes and finishes.