S-91253A585 5/16"-18 x 1 1/4" ASME B18.3 Alloy Steel Hex Drive Flat Head Screws

Key Features & Benefits at a Glance

• Exceptional tensile strength of 130,000 psi ensures reliable performance in high-stress applications, reducing the risk of fastener failure.
• Precise Class 3A thread fit provides superior engagement and vibration resistance, minimizing loosening in dynamic environments.
• Black-oxide finish on alloy steel offers enhanced corrosion resistance and a durable, non-reflective surface for long-term use.
• Fully threaded design allows for maximum grip and adjustability across the entire length, simplifying installation in various materials.
• 82° countersink angle enables a flush fit in standard countersunk holes, creating a smooth surface and improving aesthetics.
• Hex drive compatibility with a 3/16" drive size ensures easy installation and removal with common tools, reducing assembly time.
• High hardness (Rockwell C39) provides excellent wear resistance, maintaining thread integrity through repeated use.

Professional Applications & Engineering Value

This 5/16"-18 UNC flat head socket cap screw is engineered to address critical challenges in industrial assembly and machinery. The black-oxide alloy steel construction combats rust and wear, ideal for environments exposed to moisture or chemicals. Its coarse UNC threads and Class 3A fit deliver secure fastening in metals and composites, preventing backlash in vibrating equipment. The flat head with 82° countersink ensures a seamless finish in automotive, aerospace, and construction applications, where surface flatness and reliability are paramount. Fully threaded for versatile grip, it supports heavy-duty frames, enclosures, and structural components, enhancing operational safety and reducing maintenance needs.

Specification Summary & Compliance

This screw adheres to Class 3A thread tolerances for precise fit, with UNC coarse threads (5/16"-18) and right-hand direction. It meets ASME B18.3 and ASTM F835 specifications for dimensional accuracy and performance. Compliant with RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) regulations, it ensures environmental safety and material restrictions are upheld.