ASTM A193 B7 Heavy Hex Bolts 1/2"-2" Hot Dip Galvanized Heavy Hexagon Head Bolts

ASTM A193 Grade B7 Heavy Hex Bolts – 1/2″ to 2″

This product is a heavy hexagon head bolt manufactured to ASTM A193/A193M Grade B7, the standard specification for chromium-molybdenum alloy steel bolting for high-temperature and high-pressure service. The bolt is produced from AISI 4140/4142 alloy steel (1Cr-0.2Mo), quenched in oil and tempered at a minimum of 593°C (1,100°F) to develop the required strength and toughness combination. Available in diameters 1/2″ to 2″ inclusive, with heavy hex dimensions per ASME B18.2.6 and UNC coarse threads per ASME B1.1, Class 2A fit. This grade is specified across all ASME pressure classes from 150 to 2500 and is the default bolting material for carbon steel and low-alloy flanged piping systems in refineries, petrochemical plants, and power generation facilities.

What are the mechanical property and chemical composition requirements for Grade B7?

For diameters up to 2-1/2″ (64 mm), Grade B7 requires minimum tensile strength of 125 ksi (862 MPa), minimum yield strength of 105 ksi (724 MPa), minimum elongation of 16%, minimum reduction of area of 50%, and hardness range of 235–331 HB. The material is a chromium-molybdenum alloy steel with controlled chemistry: carbon 0.38–0.48%, chromium 0.80–1.10%, and molybdenum 0.15–0.25%. The Cr-Mo addition provides hardenability and elevated-temperature strength. Grade B7 retains usable strength up to a maximum continuous service temperature of 450°C (840°F); above this limit, yield strength drops rapidly due to tempering effects, and ASTM A193 B16 (Cr-Mo-V) should be specified instead. For low-temperature service below -29°C, the impact-tested ASTM A320 L7 grade is required.

What are the dimensional specifications and thread configurations for 1/2″ to 2″ heavy hex bolts?

The bolt conforms dimensionally to ASME B18.2.6 for heavy hex structural bolts, with UNC coarse pitch threads per ASME B1.1. Key dimensions include: width across flats for 1/2″ = 7/8″, 3/4″ = 1-1/4″, 1″ = 1-5/8″, 1-1/2″ = 2-3/8″, and 2″ = 3-1/8″; head height ranges from 21/64″ (1/2″) to 1-7/32″ (2″); thread length for bolts 6″ and shorter ranges from 1.00″ (1/2″) to 2.75″ (2″). The 2A thread class provides a medium-fit allowance for general assembly with standard 2B internal threads. For flange bolting applications, bolt lengths are typically determined by the ASME B16.5 stud bolt chart, which specifies length as a function of flange size, pressure class, and gasket thickness.

What are the marking, traceability, and matching nut requirements for Grade B7 bolts?

Each bolt must be permanently marked with the “B7” grade symbol and the manufacturer's identification mark in separate and distinct locations on the head. Full traceability is maintained through heat code marking, linking each fastener to its specific Mill Test Report (MTR) containing chemical and mechanical test results. Grade B7 bolts must be paired with ASTM A194 Grade 2H heavy hex nuts, which are quenched and tempered carbon steel nuts with hardness of 248–352 HB and a proof load stress of 175 ksi for sizes 1″ and under. The 2H nut is the standard companion for B7 in pressure-containing bolting applications; using a softer or mismatched nut grade undermines the joint's load-bearing capacity. Washers, where specified, are typically ASTM F436 hardened washers. Assemblies can be supplied with EN 10204 Type 3.1 inspection certificates upon request, providing full heat traceability and mechanical test records.