SAE J429 Grade 8 Hex Bolts ASME B18.2.1

SAE J429 Grade 8 hex bolts, also referred to in the market as Grade 8 hex cap screws, are inch-series fasteners for mechanically loaded joints. SAE J429 defines their material and mechanical requirements, while ASME B18.2.1 specifies the applicable head, shank, and thread dimensions.

The Grade 8 designation is identified by six radial lines on the bolt head, alongside the manufacturer’s identification mark. For nominal diameters from 1/4 in through 1-1/2 in, SAE J429 Grade 8 specifies a minimum tensile strength of 150 ksi and a minimum yield strength of 130 ksi.

These fasteners are used in automotive assemblies, heavy equipment, agricultural machinery, and industrial machinery where higher-strength inch-series bolting is required. Compared with Grade 5 fasteners under SAE J429, Grade 8 offers higher specified strength properties, making it appropriate for joints with more demanding mechanical requirements.

Selection involves more than the strength grade. Nominal diameter, UNC or UNF thread, bolt length, grip length, joint loading, and compatible nut and washer specifications must all match the application. Grade 8 hex bolts should also be distinguished from heavy hex structural bolts specified under ASME B18.2.6 and structural bolting assemblies covered by ASTM F3125; a similar strength designation does not make these products interchangeable.