My 30 hp 289cc twin racing engine uses a Tru Turn 6 1/2 inch spinner...The backplate is bolted to the hub with two 1/4-20 flathead screws..the spinner has two small notches in the bottom, 180 degrees apart, where it fits over two 4-40 setscrews in the groove...Can't slip, ever....
We use a Toyota fork lift starter motor with a 4 inch cone..Turns the engine 3000 rpm...Starts ANYTHING with just a touch.....