S-91257A195 5/8"-18 x 7 1/2" ASME B18.2.1, SAE J429 High-Strength Grade 8 Steel Hex Head Screws

Key Features & Benefits at a Glance

• Maximum load-bearing capacity with 150,000 psi tensile strength, ideal for heavy machinery and structural applications
• Superior corrosion resistance from zinc yellow-chromate plating, extending service life in harsh industrial environments
• Precise thread engagement with UNF fine threads and Class 2A fit, ensuring reliable vibration resistance and secure fastening
• Enhanced durability through Rockwell C33 hardness, maintaining structural integrity under high-stress conditions
• Optimized torque transmission with external hex drive and 15/16" head width, enabling efficient installation with standard tools
• Reduced material stress concentration through partial threading design, minimizing failure risks in dynamic load applications
• Industry-standard compliance with ASME B18.2.1 and SAE J429 specifications, guaranteeing interchangeability and quality assurance

Professional Applications & Engineering Value

Engineered for heavy-duty industrial applications, this Grade 8 hex head screw delivers exceptional performance in construction equipment, agricultural machinery, and structural assemblies where high tensile strength and vibration resistance are critical. The UNF fine thread configuration provides superior clamping force distribution compared to coarse threads, while the zinc yellow-chromate plating creates a protective barrier against oxidation and chemical exposure. The partial threading design concentrates thread engagement where needed most, reducing weight without compromising fastener integrity. With its external hex drive and substantial head dimensions, installation torque is efficiently transferred, making it ideal for high-pressure bolting applications requiring precise preload control.

Specification Summary & Compliance

This 5/8"-18 UNF hex head screw maintains Class 2A thread fit tolerances for consistent engagement and meets ASME B18.2.1 dimensional specifications. Manufactured in compliance with SAE J429 Grade 8 requirements, it delivers guaranteed mechanical properties including 150,000 psi tensile strength and Rockwell C33 hardness. The zinc yellow-chromate plating provides corrosion protection while maintaining dimensional accuracy. Fastener is partially threaded with minimum 1 3/4" thread length and overall 7 1/2" length, engineered for inch-system applications requiring heavy-duty performance and standardized compatibility.