by mary and bob » Sun Aug 05, 2018 5:40 pm
Actually Jim I did a little research and found you are mostly correct. Using info on McMaster Carr website a standard elevator bolt, 1/4" 5/16, and 3/8 has tensile strength of 70,000 psi. Same sizes, grade 5 carriage bolts have a tensile strength of 120,000 psi. Stainless steel carriage bolts in those sizes are rated at 70,000 psi. My understanding on the elevator bolts is the large flat head is the key design, to spread the load and have no protrusion above a belt, or in the Uhaul case, above the floor in the walk area. I've also heard, but didn't confirm, that Airstream uses them to attach the floor to the frame. So if anyone is concerned that 70,000 psi is not enough, then definitely go with the carriage bolts. For what it's worth, there has been no known body / frame separation on any Uhaul campers, even one that was rear ended by a big truck.