S-91257A174 1/2"-20 x 4 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 – 150,000 psi rating ensures reliable performance in high-stress applications, reducing the risk of fastener failure.
• Superior corrosion resistance – Zinc yellow-chromate plating provides durable protection against rust and environmental degradation, extending service life.
• Precise thread engagement – UNF fine threads and Class 2A fit offer excellent vibration resistance and secure fastening in demanding conditions.
• High hardness for durability – Rockwell C33 hardness minimizes wear and deformation, maintaining integrity under repeated loads.
• Optimized for heavy-duty use – Grade 8 classification and partial threading deliver robust clamping force where full threading isn't required.
• Easy installation and removal – External hex drive and standard 3/4" head width allow for straightforward tool access and high torque application.
• Industry compliance assurance – Meets ASME B18.2.1 and SAE J429 specifications, guaranteeing consistent quality and interchangeability.

Professional Applications & Engineering Value

This Grade 8 hex head screw is engineered to address critical challenges in industrial assembly, where vibration loosening and corrosion are common failures. The UNF fine thread design enhances load distribution and resists back-off under dynamic stresses, making it ideal for machinery, structural frames, and automotive components. The zinc yellow-chromate plating adds a protective barrier against moisture and chemicals, crucial for outdoor or harsh environment applications. With a partially threaded shank, it provides unthreaded grip length for precise clamping without compromising the threaded section's strength. These features, combined with 150,000 psi tensile strength, ensure long-term reliability in heavy-duty fastening scenarios, reducing maintenance and replacement costs.

Specification Summary & Compliance

This fastener adheres to Class 2A thread fit tolerances for consistent engagement and meets ASME B18.2.1 and SAE J429 standards, ensuring dimensional accuracy and performance reliability. The 1/2"-20 UNF fine thread and 4 3/4" length with partial threading are manufactured to precise specifications. It complies with common industrial regulations for material and finish quality, supporting use in regulated sectors without compatibility issues.