Abstract: A disposable, double-edged rotor knife and a disposable, double-edged bed knife for use in plastic granulating machines. The rotor knife has a general "Z" shape and is held in sandwiched engagement to the rotor of the machine by a clamp that has a wedge shaped bottom. The clamp wedges the rotor knife into a wedge shaped channel formed in the rotor when a bolt that does not pass through the rotor knife is tightened. In one embodiment, the longitudinal axis of the bolt is parallel to a plane normal to the axis of rotation of the rotor, and in a second embodiment a ten degree angle is formed between the axis of the bolt and the plane. The bed knife is keyed to the machine.