Wheel Dia. (mm) 150 200 250 75 150/200 Whetstone: 200, Dry white stone: 125 . Speed. 2850 rpm 120 rpm ... Bench Grinders and Grinding Wheels A high quality bench grinder can insure that all your tools (including chisels, shears, scissors, knives and drill bits) are kept sharp. Bench grinders are also useful for general metal shaping.