Hex & Heavy Hex Bolts — ASME B18.2.1

What are Hex & Heavy Hex Bolts?

A hex bolt has a six-sided head forged or machined on one end and a threaded shank, either partly threaded or fully threaded. Heavy hex bolts have a larger, thicker head for the same diameter, which spreads load over a bigger bearing area and suits high-strength structural joints and pressure bolting with heavy hex nuts. Hex bolts are chosen where a fixed head is convenient, such as one-side access, equipment bases and structural steel connections. For pressure flanges, stud bolts are usually specified instead.

Key features

• Hex and heavy hex heads per ASME B18.2.1; metric to ISO 4014 (part thread) and ISO 4017 (full thread)
• Heavy hex heads are ⅛" larger across flats than standard hex for the same diameter
• Grades from general purpose ASTM A307 to high-strength ASTM F3125 (A325 / A490) and A193 B7
• Stainless steel A193 B8/B8M and ISO 3506 A2/A4 options
• Supplied with matching nuts and washers as sets

Specification

Applications

• Structural steel connections and pipe racks
• Equipment and pump bases
• Pipe supports and clamps
• Valve and actuator mounting
• Plant and machinery assembly

Hex bolt vs heavy hex bolt

For the same thread diameter, a heavy hex bolt has a head ⅛" wider across flats and slightly taller than a standard hex bolt, per ASME B18.2.1. The bigger head gives more bearing area, which reduces embedment and suits high-strength structural bolts (ASTM F3125 A325 and A490 are heavy hex) and pressure bolting. Standard hex bolts are used for general assembly where loads are lower.