S-91257A600 5/16"-18 x 4 1/2" ASME B18.2.1, SAE J429 High-Strength Grade 8 Steel Hex Head Screws

Key Features & Benefits at a Glance

• Exceptional load-bearing capability with 150,000 PSI tensile strength and Rockwell C33 hardness for reliable performance in high-stress applications
• Superior corrosion protection through zinc yellow-chromate plating that extends service life in harsh industrial environments
• Optimized torque transmission via external hex drive design that prevents tool slippage during installation
• Enhanced thread engagement with Class 2A thread fit ensuring precise mating with nuts and threaded components
• Versatile partial threading allowing both secure fastening and adjustable positioning in assembly applications
• Industry-standard compatibility with UNC coarse threads that resist loosening under vibration and dynamic loads
• Regulatory compliance assurance meeting ASME, SAE, RoHS 3 and REACH standards for quality and environmental safety

Professional Applications & Engineering Value

These Grade 8 hex head screws deliver critical engineering value in demanding industrial applications where failure is not an option. The 5/16"-18 UNC coarse thread configuration provides excellent resistance to vibration loosening in heavy machinery, construction equipment, and structural assemblies. The zinc yellow-chromate plating creates a protective barrier against corrosion in outdoor or chemically aggressive environments, significantly extending maintenance intervals. With partial threading along the 4-1/2" length, these steel fasteners offer both secure clamping in the threaded section and smooth shank performance where alignment or pivot points are required. The external hex drive design ensures reliable torque application with standard tools, making installation efficient while preventing damage to the fastener head.

Specification Summary & Compliance

This high-strength hex head screw features precise Class 2A thread fit per UNC standards with 5/16"-18 coarse threading and minimum thread length of 7/8". Manufactured to Grade 8 specifications with 150,000 PSI tensile strength and Rockwell C33 hardness. Compliant with ASME B18.2.1 and SAE J429 standards for dimensional accuracy and mechanical properties. Meets RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) environmental compliance requirements.