Teeth count on spur gear:  52 teeth
Spur gear outer diameter:  53.3mm
Spur gear inner diameter:  8.0mm
Spur gear thickness at teeth: 6.6mm
Teeth count on Clutch bell:  14 teeth
Clutch bell bearing journal: 10mm
Clutch bell outer diameter:  28mm
Clutch bell inner diameter:  7.9mm

Instructions:  Remove stock HPI bushing and slipper clutch pad from the stock plastic spur gear.  Insert parts into new steel spur gear.  The clutch bell uses the stock clutch bell bearings