Structural bolts use the Heavy Hex pattern. The heads and nuts are wider across the flats (1/8" larger than standard) to provide better load distribution.
Head: Heavy Hex Structural (ASME B18.2.6)
Nut: Heavy Hex Nut (ASME B18.2.2)
Washer: ASTM F436 Hardened Washer
A307 (Standard / Machine)
A307 Grade A bolts typically use the Standard Hex pattern. These are lighter and smaller than structural bolts.