Heavy hex structural bolts are designed for steel-to-steel structural connections. Consequently, they are typically very short. ASTM A325 and ASTM A490 are the two U.S. standard structural bolt specifications. A325 and A490 bolts are produced with a heavy hex head configuration which provides a wider bearing surface over which to distribute the load. Structural bolts are specifically designed for use with heavy hex nuts in the connection of structural members (as opposed to tapped holes). The nuts for structural connections shall conform to ASTM A563 or ASTM A194. The following chart will assist in proper structural nut selection. The washers used for structural connections shall meet ASTM F436 specifications.
