S-91251A581 5/16"-18 x 3/4" ASTM A574 Alloy Steel Socket Head Screws

Key Features & Benefits at a Glance

• Exceptional tensile strength of 170,000 psi ensures reliable performance under high-stress conditions, reducing the risk of fastener failure in demanding applications.
• Superior corrosion resistance from the black-oxide finish extends service life in harsh environments, minimizing maintenance and replacement costs.
• Precise Class 3A thread fit provides tight, secure fastening with minimal backlash, enhancing assembly accuracy and vibration resistance.
• High hardness rating (Rockwell C37) offers excellent wear resistance, maintaining thread integrity and durability through repeated use.
• Hex socket drive design allows for easy installation and removal in confined spaces, improving efficiency and reducing tool slippage.
• Coarse UNC threads enable quick assembly and disassembly, saving time in production and maintenance workflows.
• Full threading along the 3/4" length ensures uniform load distribution and versatile positioning for various joint configurations.

Professional Applications & Engineering Value

This black-oxide alloy steel socket head cap screw is engineered to address common industrial challenges such as vibration loosening, corrosion-induced degradation, and high-load fatigue. The UNC coarse thread design facilitates rapid installation in automated assembly lines, while the Class 3A thread fit guarantees precise alignment in machinery, automotive, and aerospace components. Its high tensile strength and Rockwell C37 hardness make it ideal for critical applications like engine mounts, hydraulic systems, and heavy equipment, where failure is not an option. The black-oxide surface treatment provides an added layer of protection against moisture and chemicals, ensuring long-term reliability in outdoor or chemically aggressive environments without compromising on dimensional stability.

Specification Summary & Compliance

This socket head cap screw features a 5/16"-18 UNC coarse thread with a Class 3A fit for high-precision applications, and is fully threaded for consistent performance. It complies with ASTM A574 specifications for alloy steel socket head cap screws, ensuring material and manufacturing consistency. Additionally, it is RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) compliant, meeting environmental and safety standards for industrial use worldwide.