What Are Structural Bolts and How Are They Used?

Structural bolts are high-strength, heavy-duty fasteners specifically engineered for steel-to-steel connections in large-scale construction. Unlike standard hex bolts, structural bolts—primarily governed by the ASTM F3125 specification (which includes the common A325 and A490 grades)—feature a “heavy hex” head. This larger head provides a wider bearing surface to distribute heavy clamping loads more effectively across structural members. They are also designed with shorter thread lengths than standard bolts, ensuring the solid shank remains in the shear plane of the joint to maximize the connection’s integrity.

In practice, these bolts are the primary fasteners used to assemble the skeletons of skyscrapers, bridges, and industrial facilities. They are typically used in two types of joints: bearing-type connections, where the bolt resists shear forces through its body, and slip-critical connections, where the bolts are pre-tensioned to create immense clamping force. This force generates the friction necessary to prevent the joined steel plates from sliding. Because they are critical to a building’s safety, structural bolts are often subjected to rigorous testing, such as rotational capacity (ROCAP) testing, to ensure they perform reliably under the extreme stresses of modern infrastructure projects.

Manufacturing

Portland Bolt manufactures A325 and A490 heavy hex structural bolts from 1/2″ diameter through 1-1/2″ diameter, typically in lengths longer than those which are normally available in the marketplace.

Stock

Grade: F3125 Grade A325 Type 1
Diameters: 1/2″ – 1″
Lengths: 5″ maximum
Origin: Domestic
Finish: Plain and hot-dip galvanized

Bolt Length Tolerance

Structural Bolt Dimensions

Stock F3125 Grade A325 Structural Bolts