S-91257A835 5/8"-18 x 7" 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 tensile strength of 150,000 PSI, this Grade 8 screw reliably handles extreme mechanical stresses in heavy-duty assemblies.
• Superior Corrosion Protection – The zinc yellow-chromate plating offers enhanced resistance to rust and environmental degradation, extending service life in harsh conditions.
• Optimized Thread Engagement – UNF fine threading and Class 2A fit ensure precise, vibration-resistant fastening with reduced risk of cross-threading.
• High-Strength Material & Hardness – Made from hardened steel with Rockwell C33 hardness, it maintains integrity under high torque and repeated loads.
• Secure External Hex Drive – The hex head design allows for high-torque installation using standard tools, preventing slippage and ensuring tight fastening.
• Partial Threading for Versatility – The partially threaded shank provides unthreaded grip length for better clamping force distribution in structural applications.
• Industry Compliance for Reliability – Manufactured to ASME B18.2.1 and SAE J429 standards, guaranteeing consistent quality and performance in regulated environments.

Professional Applications & Engineering Value

Engineered for heavy-duty industrial applications, this Grade 8 hex head screw addresses critical challenges in machinery, construction, and automotive assemblies where high tensile strength and vibration resistance are paramount. The UNF fine thread design enhances thread engagement in tapped holes, reducing the risk of loosening under dynamic loads. Combined with a zinc yellow-chromate finish, it provides durable corrosion protection, making it suitable for outdoor or chemically exposed settings. The external hex drive facilitates easy installation with common tools, while the partial threading ensures optimal clamp load distribution across joined components. Ideal for structural frames, engine mounts, and heavy equipment, this fastener delivers reliable performance where failure is not an option.

Specification Summary & Compliance

This screw adheres to precise dimensional and performance standards, including Class 2A thread fit for consistent assembly tolerance and UNF fine thread series with 18 TPI. It meets ASME B18.2.1 and SAE J429 specifications, ensuring material composition, mechanical properties, and manufacturing quality align with industrial requirements. The product is RoHS and REACH compliant, supporting use in regulated markets without hazardous substances.