AISC


6.1. Economical Suggestions

6.1.1. Why should bolt diameters be limited to a 1-in. maximum when possible?

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. Accordingly, commonly available bolt installation equipment has been designed with a capacity to fully tension 1-in. diameter ASTM A490 bolts when required; larger bolts will usually require special equipment and/ or effort. Additionally, bolt diameters larger than 1 in. may require larger clearances, edge distances, and spacings than are standard. Therefore, bolt diameters larger than 1 in. should be avoided, when possible, to help prevent potential bolt tensioning difficulties.

6.1.2. Why should mixed use of ASTM A325 and A490 bolt grades be limited to different diameters?

If ASTM A325 and A490 bolts of the same nominal diameter are mixed on a project, there exists the possibility that the A325 bolts might be installed where the A490 bolts were required. Therefore, when ASTM A325 and A490 bolts are used on the same project, quality assurance is simplified if different diameters are used for different grades.