The Inline Fabrication flush mount base plate was designed to be routed into your bench to provide a nice, flat benchtop. However, if you don't want to route your bench top (i.e. mount it directly to the surface) you must install this shim plate to raise it up a touch to allow the quick change top plate tongues to drop in and out. NOTE: REQUIRED IF NOT ROUTING THE FLUSH MOUNT BASE INTO YOUR BENCH Mfg: Inline Fabrication