Some years ago when we were still running spring ride Hutch suspension on our trailers they went from a 7/8 to a 3/4" high tensile U bolt for weight savings. We speced our trailers with single leaf springs which broke quite often, and we always used new u-bolts. That left lots of u-bolts laying around. We have bent them in all kinds of shapes, the high tensile included, in a hydraulic press to make some special hook or something and never had one to break in the press. This leads me to believe they were no harder then 5. Grade 8 won't take much of a bend and it snaps like glass.