S-91257A745 1/2"-20 x 3 1/4" 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 a 150,000 psi tensile strength, ideal for high-stress structural and machinery applications.
• Superior corrosion resistance provided by the zinc yellow-chromate plating, extending service life in harsh or outdoor environments.
• Reliable, fine-thread engagement with the 1/2"-20 UNF thread and Class 2A fit, ensuring vibration resistance and secure fastening.
• High durability and wear resistance due to the Grade 8 steel construction and Rockwell C33 hardness, minimizing deformation under heavy loads.
• Easy installation and removal with the external hex head design, allowing for high torque application with standard tools.
• Optimized for partial threading, providing an unthreaded shank for precise clamping in assemblies without thread interference.
• Compliance with major industrial standards, including ASME B18.2.1 and SAE J429, ensuring consistent quality and interchangeability.

Professional Applications & Engineering Value

This Grade 8 hex head screw is engineered to address critical challenges in heavy-duty industrial and construction applications, where failure is not an option. The high-strength steel and Rockwell C33 hardness provide exceptional resistance to shear and tensile forces, making it suitable for structural steel connections, heavy machinery, and automotive assemblies. The zinc yellow-chromate plating offers robust protection against corrosion, significantly reducing maintenance needs in environments exposed to moisture or chemicals. With its 1/2"-20 UNF fine thread and Class 2A thread fit, it ensures precise, vibration-resistant fastening, crucial for dynamic loads. The partial threading design allows the unthreaded portion to act as a dowel, enhancing alignment and load distribution in bolted joints, thereby improving overall assembly integrity and safety.

Specification Summary & Compliance

This fastener adheres to precise dimensional and performance criteria, including a Class 2A thread fit for consistent engagement and a 1/2"-20 UNF fine thread per unified screw thread standards. It meets ASME B18.2.1 and SAE J429 specifications for hex head screws, ensuring reliability in mechanical and structural applications. The product is fully compliant with RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) regulations, confirming it is free of hazardous substances and safe for use in various industries.