Keyseat cutters (AKA woodruff cutters, keyway cutters, or T-slot cutters), are a milling tool used often by machinists to cut grooves in shafts. The grooves provide positive engagement and prevent slippage and unwanted rotation when keyed parts are mounted to the shaft. They’re also used as slot cutters. Products vary by cutter diameter, shank diameter and other dimensions, as well as by whether they are composed of high speed steel, cobalt steel, or some variation of carbide, among other considerations. For more unique milling cutters, see our dovetail cutters and indexible milling cutters.