Member 3B reported in 2012 "twelve volt starters have a 12 mm diameter shaft, six volt starters have a 14 mm shaft, hope that helps." That would be 12V = .472 and 6V = .551
Don't know if Canadian stuff is different.

This is a 2020 post by a so called guru: "if it's 5/8" you're running a 6 volt starter. 12V starters have a 1/2" diameter shaft." That would be 12V = .500 and 6V = .625

The number on your tag: 2449651 is shown on NAPA website as 6V 1949 Chevy 3100 foot start. So put it on.

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn