Wheel Stud / Lug Nut: Description and Operation

Metric wheel nuts have the word Metric stamped on the face. The letter M is stamped at the end of the metric wheel stud.
Thread size of the metric wheel nuts and studs is indicated by the following example:
M12 x 1.5
^ M = Metric
^ 12 = Diameter in millimeters
^ 1.5 = Millimeters per thread (gap between)