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 2.00in. male register on the front to keep your supercharger pulley running concentric. This pulley measures 2.250" thick and has a 5in. o.d. and is made from billet alum. included are grade 8 mounting hardware. Pulley uses six 3/8 mounting holes on a 2.782" bolt circle for mounting of supercharger pulley. fits 4-71 thru 16-71 roots or screw superchargers.