What size is that wheel stud you're trying to replace? Is it SAE or metric? And that mystery lug nut in your spares box... how can you tell M12 from 1/2" without a micrometer or a trip to the hardware store?
Thread Detective® to the rescue!
This "Lug Nut" Thread Detective has 8 special steel fittings, each with a different SAE (inch) or metric (mm) thread size. Each size has both male and female threads so you can identify both lug nuts and wheel studs (or hub threads and wheel bolts). The fittings are all strung together on a wire lanyard and connected to a small metal tag with an 85mm (3 3/8") ruler with both metric and SAE markings. The fittings are separated by shatterproof, color-coded plastic dividers (blue for metric, red for SAE). Each fitting has its thread size permanently printed in bold numbers. Loops at both ends of the lanyard let you hang it near your workbench or in the trailer. The extra-long lanyard helps to prevent you getting hung up on the neighboring studs.
This kit includes the most common thread sizes found on lug nuts and wheel bolts.
SAE (inch) sizes: 7/16-20, 1/2-20, 9/16-18
Metric (mm) sizes: M12x1.25, M12x1.5, M12x1.75, M14x1.5, M14x2.0