A melonized distributor gear at first will appear like any normal iron gear. But if you look closely, the melonized gear (left) offers a mottled appearance on the collar while a standard iron gear is smooth (right). (Image/Jeff Smith) "I believe that is a MSD Pro Billet distributor on the right. It has a fully machined billet aluminum housing with O-ring sealing grooves machined into the lower part of the housing."