descriptions by various vendors are at the best sporatic-----------but the description that says for non-roller cams may be slanted to fact that later model roller lifter equipped engine have a smaller nose and are equipped with a thrust plate to retain the cam in its position-we used to used a front button shimmed for clearance against the front cover---now the cam may have a smaller outside diameter/bolt pattern for the gear-so its an issue of the top gear fitting the nose of the cam-----