Wheel Bolts

Wheel bolts have an external male thread which screw into threaded holes on the vehicles hub whereas wheel nuts have a threaded hole which screws onto a external stud on the vehicles hub.

The size across the flats on the head of the bolt. It would also be the size socket or wheel brace you would use. The hex size is usually 17, 19, 21 or 22mm. On commercial vehicles and 4x4s this can sometimes be 24mm or 27mm.