Properly called plate-mounted wheels. To fit Baldor carbide grinders and the like.
120 is an Ok grit for lathe bits and like. ( even though 220 to way fine like 1500+ can give a much finer finish. 500 grit is the beginning of near mirror, but as you go finer the stock removal takes more time. Aluminum turning would like 220 and finer, but 120 will work.
Grinding wet is best, and try to use the high place on the wheel to keep wheel straight and flat. Try to remove all steel so as to be grinding carbide only to make wheels last longer. One of my grinding tasks at my first grinding job was grinding single-point carbide tool bits, sometimes by the hundreds+ by eyeball to a couple thousandth point dimension.
Mounting such wheels put a slip of plastic under your indicator point and indicate face run out to .001 or .002, paper is an OK shim for the back of the wheel to make true...this is so at the end of wheel life you don't end up with .010 of wasted diamonds when you run into the wheel structure material.