Our most popular 4 Bolt Spinner Hub.  The outside diameter of the hub measure 4.75" with four mounting holes on 4" centers.  That is 4" centers measuring Diagonally.  From left to right the holes are spaced at 2-7/8".

It is a 1.0" bore with a 1/4" key way and  set screw.  It also come with a "Pre-Drilled" crosshole for installation on motors that are already cross drilled. 

It can be used on most spinner discs from 12" to 24" diameter.