W.H.O. Manufacturing has both portable and stationary tub grinders in its nine-model line. The newest of the models is the P13-63XSHD-WF, which provides a horsepower range from 600 to 990 with a choice of two Caterpillar engines. Model P12-56XSHD-WF also has a choice of Caterpillar engines and provides horsepower ratings from 503 to 880. This machine uses a 12.5-foot-diameter tub (top); and a planetary gearbox powered via a hydraulic pump-and-motor system drives the tub assembly.