I've had several customers ask if they can put a 3" paddle in their Apexs. The center to center distance on a Apex chaincase is 6.875". If you subtract .5" for half the diameter of the jackshaft you get 6.375". The radius of a 7 tooth 3" driver is 3.1875" and the track is 3.25" including the belting. Those two numbers add to 6.4375". In other words the track will be hitting the jackshaft by about .0625" at rest. This won't work.