These decorative nickel plated all metal spike caps really gives your bike some attitude. They fit all the ¼ inch allenhead bolts used on the primary crankcase, transmission, cam housing, and any other place the ¼ inch socket head bolts are used. The spike head itself is ½ of an inch at its base, and the spike and pedestal combined stand 1 ? ¼ inches tall for a very impressive and unique look. They just tap on over the ¼ inch allen head bolts. Most models of bikes require approximately 20 to 30 spikes to cover the majority of the bolts on both the transmission and primary side. (a set of 9 and a set of 12 is a good starter kit) Note: Derby cover, rocker cover, and inspection plate spikes shown in pictures are sold as separate kits. These are sold in sets of 4, 9 and 12