I remember when building the LongEZ, Rutan said a 3/8” bolt was plenty enough to hold the wings on but we used ¾”. Not for the strength but for the surface area. His opinion was tighten them up enough so the nut won’t back off and leave it at that. IF they loosen over time … tighten ‘em up. Too tight will crush epoxy filled fiber. Bad deal.

It ain’t exactly an exact amount but hope it helps.

Jim