Some higher end angle grinders have speed control built in, but usually they don't. I'm borrowing a 7" Snap on angle grinder with buffing wheel that's variable speed. I probably wouldn't want to buy one. $$$$
If your angle grinder has 5/8 x 11 threads, then neither an M10 or M14 will fit. You'd need an adapter from your Standard threads to either of the two metric sizes.
