S-91266A562 1/4"-28 x 3/4" ASTM F835 Alloy Steel Thread-Locking Hex Drive Flat Head Screws

Key Features & Benefits at a Glance

• Vibration-resistant locking with permanent Nylon patch thread locker, maintaining secure fastening from -65° to 250° F without loosening
• Exceptional durability from black-oxide alloy steel construction, offering superior corrosion resistance and long service life in harsh environments
• Precision thread engagement with Class 3A UNF fine threads, ensuring reliable, tight fits and reduced risk of cross-threading in critical assemblies
• High load-bearing capacity with 130,000 psi tensile strength and Rockwell C39 hardness, supporting heavy-duty industrial applications
• Streamlined installation featuring a standard 82° countersink angle and hex drive, enabling flush mounting and easy torque application with common tools
• Full-threaded design for maximum grip length and uniform stress distribution along the entire fastener
• Regulatory compliance meeting ASTM F835, RoHS 3, and REACH standards, ensuring safety and environmental responsibility in global supply chains

Professional Applications & Engineering Value

This 1/4"-28 UNF Class 3A flat head screw is engineered to address common industrial challenges such as vibration-induced loosening and component failure in dynamic environments. The Nylon patch thread locker provides a permanent, chemical-free locking mechanism that remains effective across a wide temperature range (-65° to 250° F), eliminating the need for additional adhesives or lock washers. Manufactured from black-oxide alloy steel, it delivers enhanced corrosion resistance and surface durability while maintaining 130,000 psi tensile strength for high-stress applications. The fine UNF threads and Class 3A fit ensure precise alignment and secure fastening in machinery, automotive systems, and electronic enclosures where vibration resistance and dimensional accuracy are critical. The 82° countersink angle and hex drive facilitate seamless integration into tapered seats, providing a flush finish that minimizes protrusion and improves aerodynamic or aesthetic profiles.

Specification Summary & Compliance

This fastener maintains Class 3A thread tolerance per UNF standards, ensuring tight, precise fits for fine-thread applications. Manufacturing adheres to ASTM F835 specifications for consistency and performance. The product is fully compliant with RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) regulations, confirming the absence of restricted hazardous substances and supporting sustainable procurement practices. Threading is fully formed with a right-hand direction and 0.25" diameter, optimized for reliable engagement in high-vibration industrial settings.