What is the metric thread diameter of my crank arm pedal thread that's stripped
The vast, vast majority of pedal threads are 9/16" x 20 TPI. In nearly a decade in the bike industry I am aware of zero metric-threaded pedals (amazing, considering the lack of standardization in other parts!). The taps we use at the shop cost much more than the cost of a generic replacement crank (assuming it's the non-drive side, which it usually is).