I made some parts for a guy out of Grade 8 bolts because they had to be relatively hard, tensile strength was irrelevant. They worked fine and now he needs more but rather than using Grade 8 bolts I was thinking of using Pre-Hardened 4140. I can’t find any data which specifies the hardness of a Grade 8 bolt for a comparison. Any suggestions? If possible I don’t want to heat treat.