This tool is required to remove the clutch from certain model saws. This means you will need this tool to replace your clutch and drive sprocket. Each tool has a 19mm nut fitting so you can easily adapt a socket or bar wrench to torque. Clutches are reverse threaded, so be sure to turn the proper direction. A piston stop will help. Note: This clutch tool will not work on 385 or 390 models with spiral clutch springs. If you have a saw like that please use # HVA 504 00 23 01 Clutch Tool.