S-91257A708 7/16"-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

• Maximum Load-Bearing Capacity: Grade 8 classification and 150,000 psi tensile strength ensure reliable performance in high-stress industrial environments.
• Superior Corrosion Protection: Zinc yellow-chromate plating provides excellent rust resistance, extending service life in harsh conditions.
• Precision Thread Engagement: Class 2A thread fit and UNF fine threads offer secure, vibration-resistant fastening with reduced risk of cross-threading.
• Optimized Drive Efficiency: External hex drive with 5/8" head width enables high-torque installation using standard tools for faster assembly.
• Enhanced Durability: Rockwell C33 hardness maintains structural integrity under repeated stress and impact loads.
• Versatile Thread Design: Partial threading provides both threaded engagement and smooth shank sections for precise clamp load distribution.
• Regulatory Compliance: Meets ASME B18.2.1, SAE J429, RoHS 3, and REACH standards for quality assurance and environmental safety.

Professional Applications & Engineering Value

These Grade 8 hex head screws deliver critical engineering solutions where high tensile strength and corrosion resistance are paramount. The 7/16"-20 UNF fine thread configuration ensures superior vibration resistance in dynamic equipment, while the zinc yellow-chromate plating protects against chemical exposure and atmospheric corrosion in manufacturing, construction, and heavy machinery applications. The partially threaded design allows precise clamping force control, preventing joint loosening in structural assemblies. With 150,000 psi tensile strength and Rockwell C33 hardness, these fasteners maintain integrity under extreme mechanical stress, making them ideal for critical connections in automotive frames, industrial machinery, and structural steelwork where failure is not an option.

Specification Summary & Compliance

Manufactured to Class 2A thread fit tolerances with UNF fine thread spacing (7/16"-20), ensuring precise engagement and interchangeability. Complies with ASME B18.2.1 dimensional standards and SAE J429 material specifications for Grade 8 fasteners. Meets RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) environmental compliance requirements. Threading is partially applied with minimum 1 1/8" thread length on 3 1/4" overall length fasteners.