Steel Solutions Center
6.1. Economical Suggestions
The industry standard ¾-in., 7⁄8-in. and 1-in. bolt diameters provide adequate design strength for the vast majority of connections in steel structures, although larger bolt diameters can be used when necessary. It is recommended that one selects bolt diameters and grades to suit the loads when connections are designed. One should try to maintain a ¼-in. difference in diameters to avoid installing an undersized bolt in a joint. And one should try to use one bolt grade when possible. If more than one bolt grade is specified on a project, at least avoid specifying two different grades of bolts with the same diameter.
6.1.2. Why should mixed-use of ASTM F3125/F3125M GRADES A325 and A490 bolts be limited to different diameters?
If Grades A325 and A490 bolts of the same nominal diameter are mixed on a project, there exists the possibility that the Grade A325 bolts might be installed where Grade A490 bolts were required. Therefore, when Grades A325 and A490 bolts are used on the same project, quality assurance is simplified if different diameters are used for different grades.