crashtech
Combo Man & Mod
I don't think it's fair to blame poorly trained craftsmen for the 5/16" recommendation. The conditions under which the welds are made are not always possible to control 100%, and coatings that cause weld contamination are either in or near the weld zone. Add to that the varying thickness of material all around the vehicle but especially in structurally reinforced areas, a recommendation of 5/16" starts to make sense. Personally I like to use 9/32 on my hole punch most of the time if there is room on the flange for it, but I don't go below 1/4" unless forced to.