S-91257A597 5/16"-18 x 3 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 capacity with 150,000 PSI tensile strength, ideal for high-stress industrial applications
• Superior corrosion resistance through zinc yellow-chromate plating, extending service life in harsh environments
• Reliable mechanical performance with Rockwell C33 hardness, maintaining structural integrity under heavy loads
• Optimized installation efficiency featuring external hex drive and coarse UNC threads for faster assembly
• Precision-engineered fit with Class 2A thread tolerance ensuring consistent mating with nuts and components
• Versatile partial threading allowing both secure fastening and adjustable positioning in assemblies
• Industry-standard compliance meeting ASME B18.2.1 specifications for guaranteed interchangeability

Professional Applications & Engineering Value

These Grade 8 hex head screws deliver critical performance advantages in demanding industrial settings where failure is not an option. The zinc yellow-chromate plating provides superior barrier protection against corrosion, making these fasteners ideal for outdoor equipment, automotive assemblies, and machinery exposed to moisture or chemicals. The 5/16"-18 UNC coarse thread configuration ensures rapid installation while maintaining vibration resistance, significantly reducing assembly time in production lines. With partial threading design, engineers gain flexibility in applications requiring both clamping force and smooth shank sections. The combination of 150,000 PSI tensile strength and Rockwell C33 hardness makes these screws particularly valuable in structural frameworks, heavy equipment manufacturing, and load-bearing assemblies where mechanical reliability is paramount.

Specification Summary & Compliance

Manufactured to exacting ASME B18.2.1 standards with Class 2A thread fit tolerance for precision mating. The 5/16"-18 UNC coarse thread configuration ensures industry-standard compatibility. These Grade 8 fasteners are fully compliant with RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) environmental regulations, containing no restricted substances. The 3-1/2" length with 7/8" minimum thread length provides optimal engagement for various material thicknesses while maintaining the specified mechanical properties throughout the fastener.