Our 30 hp 289 twin racing engine has 3 bolts holding the prop on...A 3/8x24 center bolt and two 1/4x20 anti rotation bolts...It would work (and has) with only the center bolt when the other two got loose when we forgot to check between rounds...If it had been a 6 bolt hbu without the center bolt the 6 would have sheared off and the plane would have been destroyed...As it happened the center bolt got tighter when the other 2 sheared...NO six bolt hubs for me......
A 3/8x24 grade 8 center bolt will hold ANY prop on ANY rc airplane ever made...
The key word is TIGHT..
The prop was a CF 21x28 turning at 9000 rpm....