what they do is slightly change the pitch just enough to keep the spurs the same size. but in doing this i find certain spurs last longer than others. the pitch change is so the size of the spur stays the same as doc noted, but with a tooth count difference. i can show you next time your at the track Mark. biggest diff is my ED pinions. my 16t compared to my 15t, extremely noticable.
Serpent - Walter RC
Serpent E Power ..... Serpent 747 Reds M3T
Serpent 966-TE Reds M7T .... S411ERYX Speedpassion 3.5T, T-Shox
Serpent 811-TE REDs R5T