Originally Posted by MotorBicycleRacing
Probably 4 mm.
Use one of the 4 mm magneto cover bolts to check the size.
I was thinking its 3mm but it could be 4mm, and who knows like other things some may be 4mm and some may be 3mm....lol
For sure using a mag cover screw to see if its just right or to big is a good way to norrow it down.