I have a Puch 1980 vintage and am having trouble determining the correct motor to back tire drive chain. I know its 12.70 mm pitch which is 1/2 inch. I am assuming that I need to buy metric chain. The catelog I have (mcmaster carr) calls out two sizes in that pitch, one with a roller width 3.18mm and one with a width of 7.75mm (.125, .305). My existing chain appears to have a roller width of around .187.
Any thoughts, Thanks Steve