S-91257A594 5/16"-18 x 3 1/4" ASME B18.2.1, SAE J429 High-Strength Grade 8 Steel Hex Head Screws

Key Features & Benefits at a Glance

• Maximum load-bearing capability with Grade 8 classification and 150,000 psi tensile strength for critical structural applications
• Superior corrosion protection through zinc yellow-chromate plating that withstands harsh industrial environments
• Optimized thread engagement with Class 2A UNC coarse threads ensuring reliable fastening in various materials
• Enhanced installation efficiency featuring external hex drive design for secure tool grip and torque application
• Precision manufacturing complying with ASME B18.2.1 and SAE J429 standards for consistent quality and performance
• Extended service life with Rockwell C33 hardness providing excellent wear resistance and durability
• Versatile partial threading allowing both secure clamping and adjustable positioning in assembly applications

Professional Applications & Engineering Value

Engineered for demanding industrial applications, these Grade 8 hex head screws deliver exceptional performance in heavy machinery, structural steel connections, and high-vibration environments. The 5/16"-18 UNC coarse thread pattern provides superior pull-out resistance in both metal and composite materials, while the partial threading design allows for precise adjustment and clamping force distribution. The zinc yellow-chromate plating creates a protective barrier against corrosion, significantly extending service life in outdoor or chemically aggressive settings. With external hex drive configuration and substantial 3-1/4" length, these fasteners enable efficient installation in confined spaces and maintain integrity under extreme mechanical stress, making them ideal for construction, automotive, and manufacturing applications where reliability is paramount.

Specification Summary & Compliance

This Grade 8 hex head screw features precise Class 2A thread fit with 5/16"-18 UNC coarse threading and 0.3125" thread diameter. Manufactured to ASME B18.2.1 and SAE J429 specifications, ensuring dimensional accuracy and mechanical properties. The fastener is fully compliant with RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) environmental regulations, containing no restricted substances. With Rockwell C33 hardness and 150,000 psi tensile strength, this partially threaded screw maintains consistent performance across industrial applications while meeting international quality and safety standards.