†Item shown in picture may not represent exact product . Thrust buttons, also called cam buttons or thrust plugs, keep a roller camshaft from walking in the engine. They are a crucial part when retrofitting certain factory non-roller engines with a roller cam. In flat-tappet engines, the cam lobe taper that causes the lifters to spin also counteracts the forward thrust caused by the distributor drive gear. Roller cam lobes have no taper, resulting in excessive 'cam walk.' Some engines are factory equipped with a camshaft retention plate to keep the cam in place, but those that aren't require a thrust button to keep the cam in place. The 'head' end is inserted into the center hole of the cam sprocket and the 'tail' end thrusts against the timing cover, keeping the cam in place.Rollerized thrust buttons have a series of miniature Torrington bearings that allow the head of the plug to spin independently of the body, greatly reducing friction and timing cover wear.DETAILSMake: ChevroletEngine: Mark IV & V Big Block V8 w/o OE hyd roller camStyle: RollerizedMaterial: Heat-treated SteelLength: 0.950" Head O.D.: 0.875" Body O.D.: 0.700"Notes: Center bore of the cam sprocket must be at least 0.875". Your sprocket may require the bore to be enlarged. Always check for proper clearances & endplay before final assembly. **If you have any questions in regards to the compatibility with your set-up please call before you purchase**