These kits contain 4 spike bolt covers and 4 stainless steel ¼ inch bolts to replace the stock round head bolts. These spikes are made to be removable for routine maintenance and are held in place with a small amount of RTV or similar type adhesive (not included). The spikes are 1/2 inch in diameter at the base of the spike head. The TALL spikes extend 1 inch beyond the top of the bolt head for a very impressive and unique look. (1.3 inches total length). The LOW PROFILE spikes mount flush against the surface and are 3/4 of an inch tall (not shown in pictures). These use the same spike head, they just don?t have the pedestal. NOTE: The heel shifter will NOT clear the top left spike on the flush style inspection plate. Please be sure to specify if you want the tall or low spikes.