As standard these locks come with a mild steel (chocolate!) nut that tends to strip threads and round off as soon as you go near them with a spanner. The long steel nuts are 15mm end to end so cover most of the exposed thread saving it from damage.
We prefer the rubber locks to the metal ones, mainly due to the fact that I broke a brand new quality(!) metal one when tightening it up to the correct torque and had to remove & refit the tyre