pinion ?
 

does mike have mod 1 pinions with the 10th scale size motor shaft ? or do i use the bore reducer ? and witch size ? got one of the new jammin scrt 's , 1/8th scale center diff but a 10th scale motor .

You'd need to use the 1/8 bore reducer to fit the 1/8 shaft

Yes, not many 1/8 bore mod 1 pinions out there, and none that I know of that are hardened for use with a steel spur. Get the bore reducer and rcm pinions, best way to go. Until you break the 1/8 shaft on the motor, then you can get a good motor with a 5mm shaft and use the pinions w/o the bore reducer.