This specification covers the chemical, mechanical, and metallurgical requirements for two types of heavy hex structural bolts made of quenched and tempered alloy steel and having specified tensile strengths and sizes. These bolts are intended for use in structural connections, and are furnished in nominal bolt diameters M12 through M36. They are designated by type denoting chemical composition as follows: Type 1-medium carbon alloy steel; and Type 3-weathering steel. The bolts shall conform to chemical requirements as examined by heat and product analysis. The bolts shall also be tested, and shall conform accordingly to specified requirements for mechanical properties such as Brinell hardness, Rockwell hardness, microhardness, tensile strength, yield strength, elongation, reduction of area, stress area, tensile load, and proof load; metallurgical properties such as carburization and decarburization; and dimensional properties such that for the head and body, and threads. The bolts shall undergo magnetic particle inspection as well for longitudinal discontinuities and transverse cracks.