Since all roller cam lobes are ground flat instead of tapered like a hydraulic or solid cam, it is necessary to provide some means of holding the cam back to the rear of the engine. The thrust button rides between the front of the timing gear and the back of the front cover, and can be shimmed for proper end play in the cam. COMP Cams® has available both the solid nylon button and the roller thrust bearing, for the ultimate in preformance.