I worked at a weld shop. We used the 6" wheels. I bought a bigger guard off E-bay for my grinder
and that's all I've used since. I use over 100 wheels a year and I use them until they don't reach the
work then I give them to my friend for his 4" grinder. Wheels cost under $1 each when buying 100
at a time on E-bay...
I just looked that up... I never give though about it... This is what I googled and found.
4-1/2" grinder 8000 rpm
6" grinder No Load Speed 9000 RPM .
6" cut off wheel. 10,200 rpm
4" cut off wheel. 13,300
Looks like I'm OK....