Hmmmm..I guess the single 3/8-24 grade 8 bolt on my 32 hp 289 race engine should have broken instead of just holding the prop on when the two 1/4-20 thru bolts sheared.The bolt goes all the way thru the hub into the steel crank.It CLAMPS the prop on the hub, the 1/4-20s keep it from slipping..You can put a lotta torque on a 3/8 bolt....When the carbon prop compressed they ALL got loose, the single bolt still held the prop on..The data logger on the engine showed that it was turning a 27 pitch two blade prop 9000 rpm at the time, a pretty good test.........A grade 8 bolt has a minimum tensile strength of 150,000 lbs...It would be hard to even break one with a sledge hammer, much less shear it off....When a single bolt without anti rotation bolts or pins comes loose the prop just comes off.....Only single bolt I ever saw break was a grade 5 I had tapped for a 10-32 spinner bolt, the head came off where it was thinner under the hex....Never used a grade 5 again for a prop bolt.....[8D
FWIW...At our races we run G62s, GT80s, Aerrow 200s, Herbrandson 289s, and a few others..Not a 6 bolt hub in the bunch, 64 planes at the last race...We don't want all those extra holes in the props...the GT80s are turning 11,500 rpm, the Aerrow 200s about 10,500 and making 180 degree turns at 200+ mph....You think a 20 hp Giant Scale engine turning 6000 rpm puts more stress on a prop bolt/s than that ? Hardly ..[8D]