I wonder where the shear force comes from when the bolt is in the center of the prop...Our race plane hit the ground at about 200 mph when the spinner came off and hit the prop, breaking off one blade....The engine was completely destroyed, both cylinders torn off, the crankcase demolished, one carb broken completely in half, both pistons broken and the con rods bent back at a 45 degree angle..Only useable parts left were the wrist pins and bearings and one carb...The 3/8 bolt in the center of the hub was still intact and tight....FWIW..There was no mention of a single bolt being sheared off in the "bolts sheared" posts here on RCU...Mostly 6 bolt 3W and ZDZ engines....
The "average joe" would do well to check his 6 bolt prop hubs more often....Or leave 'em loose, I get $20 to fix the 3W sheared bolt hubs