Small Metric Screws and Rim Fasteners

Reading M4 x 10: diameter, length and head shape

M4 x 10 means a 4 mm thread diameter and a 10 mm length. Listings sometimes add the pitch, as in M3 x 0.5, which is the distance between thread crests. Countersunk screws are measured overall, head included, so they sit flush in a countersunk hole; pan and cap heads are measured from under the head. Phillips, hex socket and knurled thumb heads suit different tools and access.

Material and strength: brass-tone, stainless or 12.9 steel

Stainless steel resists rust, which suits visible trim, but it is softer than hardened steel. Alloy steel in property class 12.9 is very strong and hard, and needs a coating such as black oxide to resist corrosion. Brass-tone finishes are decorative. Use these for panels, covers and light assemblies, never in place of wheel studs or lug nuts, which have their own thread and strength requirements.

Questions about Small Metric Screws and Rim Fasteners

What does 12.9 mean on a screw?

It is the property class, a strength rating. A 12.9 alloy steel screw is very hard and strong, but it can be brittle if overloaded or bent, and it needs a coating to resist rust.

Countersunk or pan head: which should I choose?

Choose countersunk when the head must sit flush in a countersunk hole. Choose pan or cap heads when the surface is flat and you want a raised head with good drive contact.

Can these screws replace wheel lug bolts?

No. Wheel hardware has specific thread sizes, seat shapes and strength grades. Small screws like these are for trim, panels and light assemblies and are not made to hold a wheel.