S-91257A120 5/16"-18 x 5 3/4" ASME B18.2.1, SAE J429 High-Strength Grade 8 Steel Hex Head Screws

Key Features & Benefits at a Glance

• Exceptional tensile strength of 150,000 psi ensures reliable performance under extreme loads, reducing the risk of fastener failure in demanding applications.
• Superior corrosion resistance from the zinc yellow-chromate plating extends service life, even in harsh or outdoor industrial environments.
• High hardness rating (Rockwell C33) provides excellent wear resistance and durability, maintaining thread integrity through repeated use.
• Coarse UNC threading and Class 2A fit allow for faster assembly and easier engagement, saving time in high-volume production settings.
• Partially threaded design offers optimal clamping force on specific joint areas, enhancing structural stability in heavy machinery.
• External hex drive enables high-torque installation with common tools, streamlining maintenance and assembly processes.
• Compliance with ASME B18.2.1 and SAE J429 guarantees consistent quality and interchangeability, meeting rigorous industrial standards.

Professional Applications & Engineering Value

This Grade 8 hex head screw is engineered to address critical challenges in heavy-duty applications, such as construction equipment, automotive assemblies, and industrial machinery. The zinc yellow-chromate plated steel provides a robust barrier against rust and corrosion, essential for outdoor or high-moisture environments. With its 5/16"-18 UNC coarse thread and Class 2A thread fit, it ensures quick, secure fastening even in vibrating conditions, minimizing loosening over time. The partial threading concentrates clamping force where needed, preventing joint slippage and enhancing overall structural integrity. Ideal for scenarios demanding high tensile strength and long-term reliability, this screw reduces maintenance downtime and boosts operational efficiency.

Specification Summary & Compliance

This fastener adheres to Class 2A thread fit tolerances for consistent engagement and meets ASME B18.2.1 and SAE J429 specifications, ensuring dimensional accuracy and performance reliability. Manufactured from high-strength steel with a zinc yellow-chromate finish, it complies with industry standards for corrosion protection and mechanical properties. The product is designed for use in inch-system applications, with precise thread dimensions (e.g., 5/16"-18 UNC coarse thread) and a partially threaded configuration to support various engineering requirements.