Joe and Jon... yes. Good idea on the use of bits, Joe. Never thought of that. I'da just eyeballed it and bought a few "close ones" if I couldn't find one in my tickle trunk... which is getting harder to do those days, as Joe cited.

One other "source" might be a website for parts info. Or a manual at a shop that sells that brand of lawnmower.

Good luck with it. It's always a consternation dealing with such.