The multi bolt hubs were around with the first Q35s...The had something in the instructions about using the bolts to make the prop tips track exactly the same...All the A&Ms until the 2.0 had the six bolt hub, some with a single stud adapter...All the early G38s had drilled and tapped holes in the steel hub, but came with a single bolt....I like single bolts hubs better than six bolt, a 3/8-24 grade 8 or 9 prop bolt will hold ANY prop up to and including my 289cc twin racing engines...We use the single bolt to hold both the prop hub on the taper and the prop onto the hub..There is no key in the hub, just the taper..We put two 1/4-20 bolts thru the prop into the hub to keep it from slipping, but the single bolt would hold it with no problems if the two 14-20s were only partly into the prop...[8D]