This v-pulley serves two purposes. First it allows mounting of a blower pulley to a dampner without having to drill the blower pulley. It also allows three acc. to be driven with a v-belt. The pulley has a register on the back that fits in the dampner as well as a 2.00" male register on the front to keep your supercharger pulley running concentric. This pulley measures 2.250" thick, has a 5.00" o.d. and is made from billet alum. that is hard anodized for wear resistance and longevity. Grade eight mounting hardware is included. This pulley uses six 3/8" mounting holes on a 2.782" bolt circle for mounting of supercharger pulley. Fits 4-71 thru 16-71 supercharger.