S-91257A831 5/8"-18 x 3 3/4" ASME B18.2.1, SAE J429 High-Strength Grade 8 Steel Hex Head Screws

Key Features & Benefits at a Glance

• Exceptional tensile strength of 150,000 psi ensures reliable performance in high-stress applications, reducing the risk of fastener failure.
• Superior corrosion resistance with zinc yellow-chromate plating extends service life in harsh or outdoor environments.
• High hardness rating (Rockwell C33) provides excellent wear resistance and durability under repeated use.
• Precise Class 2A thread fit allows for smooth assembly and secure fastening, minimizing cross-threading issues.
• Partially threaded design offers optimal grip and clamping force where full threading isn't required.
• External hex drive enables easy installation and removal with standard tools, improving maintenance efficiency.
• Compliance with major standards including ASME B18.2.1 and SAE J429 ensures consistent quality and interchangeability.

Professional Applications & Engineering Value

This Grade 8 hex head screw delivers critical reliability in demanding industrial settings where failure isn't an option. The 5/8"-18 UNF fine thread configuration provides superior vibration resistance compared to coarse threads, making it ideal for machinery, structural assemblies, and heavy equipment subjected to dynamic loads. The zinc yellow-chromate plating creates a robust barrier against corrosion while maintaining electrical conductivity for grounding applications. Engineers specify this partially threaded fastener for applications requiring precise clamp load distribution, as the unthreaded shank section bears against connected materials without thread engagement. With its 150,000 psi tensile strength and Rockwell C33 hardness, this screw solves common challenges in construction, automotive, and manufacturing where both mechanical strength and environmental resistance are paramount.

Specification Summary & Compliance

This fastener maintains Class 2A thread fit tolerances per UNF standards with a 5/8"-18 thread size and 3 3/4" length. Manufacturing complies with ASME B18.2.1 and SAE J429 Grade 8 specifications for dimensional accuracy and mechanical properties. The product is fully compliant with RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) environmental regulations, containing no restricted substances above threshold limits.