S-91268A529 5/16"-18 x 5 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 Grade 8 classification and 150,000 psi tensile strength for reliable performance in high-stress applications
• Superior corrosion resistance thanks to the black-oxide finish that protects against rust and extends service life in harsh environments
• Optimized thread engagement with UNC coarse threading and Class 2A fit ensuring secure fastening and reduced cross-threading risk
• Enhanced torque transmission through the external hex drive design that provides positive grip with standard tools
• Reduced material stress concentration through Rockwell C33 hardness balance between strength and ductility
• Versatile partial threading allowing both secure clamping and adjustable positioning in assembly applications
• Regulatory compliance assurance meeting ASME B18.2.1 specifications and environmental standards including RoHS 3 and REACH

Professional Applications & Engineering Value

These Grade 8 hex head screws deliver critical engineering solutions where failure is not an option. The black-oxide steel construction provides essential corrosion protection for industrial equipment exposed to moisture and chemicals, while the UNC coarse thread design ensures rapid installation and superior vibration resistance in heavy machinery, structural steel connections, and construction applications. The 5 1/2" length with partial threading offers optimal grip range for thick material assemblies, and the external hex drive enables high-torque installation without stripping. Engineered to withstand extreme mechanical stresses, these heavy-duty fasteners prevent joint failure in critical applications from manufacturing equipment to infrastructure projects.

Specification Summary & Compliance

This 5/16"-18 x 5 1/2" hex head screw features precision UNC coarse threads with Class 2A thread fit tolerance for consistent engagement. Manufactured to ASME B18.2.1 specifications with Grade 8 strength certification, ensuring dimensional accuracy and mechanical performance. The fastener is fully compliant with RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) environmental regulations, making it suitable for global industrial applications requiring verified material safety standards.