S-91266A571 1/4"-28 x 1 1/2" 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 ensures reliable fastening in high-stress environments.
• Exceptional tensile strength of 130,000 psi provides superior load-bearing capacity for demanding industrial applications.
• Precise Class 3A fine threading delivers secure, tight fits with minimal risk of cross-threading or loosening.
• Durable black-oxide alloy steel construction offers enhanced corrosion resistance and long-term reliability.
• Wide temperature tolerance from -65° to 250°F maintains performance in extreme operating conditions.
• 82° countersink angle and flat head design enables flush mounting for streamlined, professional finishes.
• Hex drive compatibility with 5/32" drive size allows for efficient installation and removal with standard tools.

Professional Applications & Engineering Value

This 1/4"-28 UNF flat head screw is engineered to address critical challenges in industrial assembly, where vibration-induced loosening and material fatigue are common concerns. The nylon patch thread locker provides a permanent locking mechanism that eliminates the need for secondary adhesives, reducing assembly time and improving reliability. Manufactured from black-oxide alloy steel, it combines high Rockwell C39 hardness with excellent corrosion resistance, making it ideal for machinery, automotive, and aerospace applications. The Class 3A fine threading ensures precise engagement in tapped holes, while the fully threaded design maximizes grip length. These features make it a top choice for engineers seeking durable, compliant fasteners that withstand harsh environments and maintain integrity under dynamic loads.

Specification Summary & Compliance

This screw meets ASTM F835 specifications for dimensional accuracy and performance. It features UNF fine threading with a Class 3A thread fit for superior precision. The product is fully compliant with RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) regulations, ensuring environmental safety and material sustainability. Additional specifications include a right-hand thread direction, 82° countersink angle, and fully threaded design for consistent application across industrial standards.