The Cap-A-Dapts will install on most MSD Pro-Billet Distributors (except the Ford FE, PN 8594). Both kits are supplied with a high quality cap with brass terminals, rotor and cap spacer. The rotor is injection molded out of Rynite® for incredible strength and resistance to spark. Thick vanes are incorporated to stir up the air in the cap for even more ionization prevention. Three Cap-A-Dapts are available; two with a fixed rotor and another with an adjustable, two-piece rotor. The two-piece rotor allows you to adjust the rotor tip to cap terminal alignment so you can adjust the rotor phasing. All of the MSD Distributors are phased at the factory, but if you are running a Multi-Step Retard or Timing Controller, having the ability to adjust the rotor phasing is beneficial. The MSD Cap-A-Dapt adapts a large, Ford style cap onto your MSD distributor. This large cap spaces the spark plug terminals farther apart which lessens the chances of cross-fire and ionization occurring.