S-91251A558 1/4"-20 x 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 critical assemblies.
• Superior corrosion resistance from the black-oxide finish prolongs service life in harsh environments, minimizing maintenance and replacement costs.
• Precise Class 3A thread fit provides secure, vibration-resistant connections, enhancing assembly integrity and reducing loosening over time.
• Partially threaded design allows for controlled clamping force and easier alignment, ideal for applications requiring specific grip lengths.
• High hardness (Rockwell C37) offers excellent wear resistance, maintaining thread integrity and drive features through repeated use.
• Hex socket drive enables high-torque installation with standard tools, facilitating efficient assembly and disassembly in confined spaces.
• Compliance with ASTM A574, RoHS 3, and REACH ensures material consistency, environmental safety, and suitability for regulated industries.

Professional Applications & Engineering Value

These black-oxide alloy steel socket head cap screws are engineered to address common industrial challenges such as vibration-induced loosening, corrosion in humid or chemical environments, and the need for high clamping force in compact assemblies. The UNRC coarse thread and Class 3A fit provide rapid installation and reliable seating in materials like steel or aluminum, reducing assembly time while maintaining joint security. With a partially threaded shank, they excel in applications where precise unthreaded grip length is critical, such as in machinery frames, automotive components, and heavy equipment. The combination of 170,000 psi tensile strength and Rockwell C37 hardness ensures durability in dynamic load conditions, making them a trusted choice for OEMs and maintenance teams seeking long-term fastener performance without frequent replacements.

Specification Summary & Compliance

This socket head cap screw features a 1/4"-20 thread size with Class 3A thread fit for precise dimensional accuracy, and is manufactured to ASTM A574 specifications for consistent quality. It complies with RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) regulations, ensuring it is free from hazardous substances and suitable for global industrial use. The screw is supplied in the inch system with a coarse thread spacing and right-hand thread direction, adhering to standard UNRC threading for broad compatibility.