HDG or Galvanized Heavy Hex Bolts/Steel Structure Bolts ASTM A325

Heavy hex bolts have a head that is larger than a standard (finish) hex head. Standard heavy hex bolts are made of low to mid carbon steel. The large head offers a greater bearing surface that distributes the clamping load over a greater area.
Heavy hex structural bolts are designed for steel-to-steel structural connections. Consequently, they are typically very short. The A325 and A490 specifications are not intended for general applications, including anchor bolts. In these applications, substitutions of A449 for A325 and A354 grade BD for A490 should be considered.

Heavy hex structural bolts are designed for steel-to-steel structural connections. The ASTM A325 and A490 specifications cover high strength heavy hex structural bolts from 1/2" diameter through 1-1/2" diameter. These bolts are intended for use in structural connections and therefore have shorter thread lengths than standard hex bolts. The A325 and A490 specifications are not intended for general applications.

The ASTM A490 specification covers quenched and tempered, alloy steel, heavy hex structural bolts from 1/2" diameter through 1-1/2" diameter with a minimum 150 ksi tensile. A490 bolts are similar in application and dimensions to A325 Hex Cap Screws heavy hex structural bolts but are made from an alloy steel rather than a medium carbon steel, resulting in a higher strength fastener.