I am trying to remove the starter on my Craftsman mower. It has a B&S 12.5 hp I/C engine about 12 yrs old. I need to replace the cog wheel on top of the starter. My cheapo hex key set will not fit, what size specifically do I need to remove the two bolts holding the starter?

Hex, torx and bristol look very similar. I haven't seen bristol stuff for quite a while.

For hex, you can just measure across the flats.

Torx looks like a star but tapered inward. I think it's measured in metric. Thus a T-6 is 6 mm point to point.

Then there is metric version of the allen wrench.