S-91670A542 1/4"-20 x 1" ASTM A574 Left-Hand Threaded Alloy Steel Socket Head Screws

Key Features & Benefits at a Glance

• Exceptional tensile strength of 170,000 PSI ensures reliable performance in high-stress applications, reducing the risk of fastener failure.
• Left-hand UNC coarse thread design provides secure fastening in specialized assemblies where reverse threading is required for safety and functionality.
• Black-oxide surface treatment on alloy steel offers enhanced corrosion resistance, extending service life in harsh industrial environments.
• Class 3A thread fit guarantees precise, tight tolerances for superior engagement and vibration resistance in critical machinery.
• Hex socket drive (3/16") allows for high-torque installation with standard tools, improving assembly efficiency and reducing strip-out risks.
• Full threading along the 1" length ensures consistent grip and load distribution across the entire fastener, maximizing holding power.
• Compliance with ASTM A574, RoHS 3, and REACH assures material quality and environmental safety, meeting rigorous industry and regulatory standards.

Professional Applications & Engineering Value

Engineered for demanding industrial settings, these left-hand thread socket head cap screws address critical assembly challenges where standard right-hand threads are unsuitable. The black-oxide alloy steel construction, combined with a Rockwell C37 hardness rating, provides exceptional durability against wear and environmental exposure, making them ideal for machinery, automotive, and aerospace components that require reverse-threading mechanisms. The coarse UNC thread and Class 3A fit ensure rapid installation and high vibration resistance, reducing maintenance needs in dynamic operations. These screws are particularly valuable in applications like rotating equipment or safety-critical assemblies, where their left-hand direction prevents loosening under counter-clockwise forces, enhancing operational reliability and minimizing downtime.

Specification Summary & Compliance

This socket head cap screw features a 1/4"-20 UNC left-hand thread with a Class 3A thread fit for precise dimensional accuracy and tight tolerances. It is manufactured in accordance with ASTM A574 specifications, ensuring consistent material and mechanical properties. The product is fully compliant with RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) regulations, confirming adherence to environmental and health safety standards for industrial use.