S-91670A581 5/16"-18 x 3/4" 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 under high-stress conditions, reducing the risk of fastener failure.
• Superior corrosion resistance from the black-oxide finish extends service life in harsh industrial environments, minimizing maintenance needs.
• Precise Class 3A thread fit provides tight, secure connections with minimal backlash, enhancing assembly accuracy and vibration resistance.
• Left-hand threading offers specialized functionality for applications requiring reverse-threading security, preventing unintended loosening in rotating machinery.
• High hardness rating (Rockwell C37) maintains thread integrity and drive socket durability during repeated installation and removal cycles.
• Full threading along the entire 3/4" length allows flexible positioning and maximum grip in deep or variable material thicknesses.
• Standard hex drive compatibility with common 1/4" tools enables quick installation and removal while minimizing strip-out risks.

Professional Applications & Engineering Value

This black-oxide alloy steel socket head cap screw delivers critical performance where standard fasteners fail. The left-hand UNC coarse thread configuration provides intentional reverse-threading protection in rotating equipment, machinery, and automotive systems where right-hand rotation could loosen conventional fasteners. Engineered with Class 3A thread fit precision, it eliminates play in high-vibration environments while the fully threaded design accommodates varying material thicknesses without compromising clamp force. The black-oxide surface treatment creates a durable barrier against moisture and chemicals, making these socket head cap screws ideal for manufacturing equipment, industrial automation, and outdoor applications requiring both corrosion resistance and 170,000 psi tensile strength.

Specification Summary & Compliance

Manufactured to ASTM A574 specifications with Class 3A thread fit tolerances for precision assembly. Features 5/16"-18 UNC coarse threads in left-hand orientation with 0.3125" thread diameter and 3/4" fully threaded length. Compliant with RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) environmental regulations, ensuring safe use in regulated industries.