[BrianG]

Dunno. Since there are different methods to creating hardened pinions (hardening regular pinions vs using a modded clutchbell), you'd have to look at how the pinions are shaped I would guess.

Both clutchbell type and hardened "regular" pinions work fine on a plastic and steel spur, but a hardened version of a regular pinion does not work well at all on a steel spur. Mike's hardened pinions work on either steel or plastic.