S-91257A122 5/16"-18 x 9" ASME B18.2.1, SAE J429 High-Strength Grade 8 Steel Hex Head Screws

Key Features & Benefits at a Glance

• Maximum Load Capacity: With a tensile strength of 150,000 psi, this screw withstands extreme forces in heavy machinery and structural applications.
• Superior Corrosion Resistance: Zinc yellow-chromate plating provides excellent protection against rust and environmental degradation, extending service life.
• High-Strength Material: Grade 8 steel with Rockwell C33 hardness ensures exceptional durability and resistance to wear under high stress.
• Reliable Fastening: UNC coarse threading and Class 2A thread fit offer secure, vibration-resistant connections in coarse-thread applications.
• Easy Installation: External hex drive and standard 1/2" head width allow for straightforward tightening with common tools, reducing assembly time.
• Industry Compliance: Meets ASME B18.2.1 and SAE J429 specifications, ensuring consistent quality and performance in industrial settings.
• Optimized Thread Design: Partially threaded shank with a minimum thread length of 1 1/8" provides focused grip strength where needed, minimizing material stress.

Professional Applications & Engineering Value

This Grade 8 hex head screw is engineered for demanding environments where failure is not an option. Its high tensile strength and Rockwell C33 hardness make it ideal for heavy machinery, construction frameworks, and automotive assemblies, addressing common issues like joint loosening under dynamic loads. The zinc yellow-chromate plating combats corrosion in humid or outdoor settings, while the UNC coarse thread ensures quick, secure fastening in coarse-threaded materials, reducing the risk of cross-threading. With a 9-inch length and external hex drive, it simplifies installation in tight spaces, enhancing efficiency in industrial maintenance and manufacturing projects. This screw delivers reliable performance in applications requiring ASME B18.2.1 compliance, such as structural bolting and equipment mounting.

Specification Summary & Compliance

This fastener adheres to precise dimensional standards, including a Class 2A thread fit for consistent assembly and UNC coarse threading with a thread size of 5/16"-18. It meets ASME B18.2.1 and SAE J429 specifications, ensuring compatibility with industrial requirements. The zinc yellow-chromate finish provides environmental protection, and the Grade 8 classification confirms high strength and durability. Compliance with general industry standards supports use in applications demanding reliability and safety.