I mounted one last year, and I love it. It was self-standing with a cast iron stand before. It's a rather large motor (I think around 1kw). The fastening holes were M10. However, I have a concrete wall, and I drilled right through it, and used threaded rods to attach it. I also made a hole for the nut on the other side, so I was able to fill it all up with concrete from the back and it isn't visible (basivally, the nut is inside the wall now). There's also a piece of rubber I put between the grinder and the wall, so it sits nice and firmly and there are no vibrations at all.
I'm not sure how secure it'd be with various types of inserts, but if you can just drill through the wall it's surely the most secure way.
I mounted some trash can wheels on the leftover stand, and fitted a vise on top. It's also amazing, and I mounted the wheels so they go on the ground only when I tip it over enough, just like a trash can. It's a lot more portable and heavy enough that I can do a lot of stuff on it easily.