S-91205A581 5/16"-18 x 3/4" ASME B18.3, ASTM A574 Alloy Steel Thread-Locking Socket Head Screws

Key Features & Benefits at a Glance

• Vibration-resistant locking: Integrated nylon patch thread locker ensures secure, permanent fastening in high-vibration environments, eliminating the need for separate locking hardware.
• Exceptional strength for demanding applications: Manufactured from alloy steel with a 170,000 psi tensile strength and Rockwell C37 hardness to withstand extreme loads and prevent shear failure.
• Superior corrosion protection: The black-oxide finish provides a durable layer of defense against rust and corrosion, extending the screw's service life in harsh conditions.
• Precision-engineered thread fit: Class 3A thread fit with UNC coarse threads offers tighter tolerances for a more secure and reliable connection compared to standard fits.
• Wide operational temperature range: The nylon patch locker remains effective from -70° to 250° F, ensuring performance stability across diverse industrial environments.
• Optimized for high-torque applications: The standard hex socket drive and socket head design allow for high tightening torque and a low-profile installation in confined spaces.
• Guaranteed reliability and compliance: Meets ASME B18.3 specifications and is RoHS 3 & REACH compliant, ensuring material quality and environmental safety for global supply chains.

Professional Applications & Engineering Value

This Black-Oxide Alloy Steel Socket Head Cap Screw is engineered to solve critical challenges in high-stakes assembly. Its core value lies in combining high tensile strength with a permanent nylon patch thread locker, directly addressing the common industrial problem of fastener loosening due to vibration and dynamic loads. The UNC coarse thread and Class 3A fit ensure rapid assembly and a precise, secure fit, reducing the risk of cross-threading and assembly errors. This makes it an indispensable component in machinery, automotive subsystems, and heavy-duty equipment where joint integrity is non-negotiable. The corrosion-resistant black-oxide surface treatment further enhances its durability, making it a reliable, long-term solution for engineers specifying fasteners for demanding operational environments.

Specification Summary & Compliance

This fastener adheres to strict dimensional and performance standards. The thread system is 5/16"-18 UNC with a precision Class 3A thread fit. It is manufactured to the ASME B18.3 specification from Alloy Steel (ASTM A574). The product is fully compliant with RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) regulations, confirming its suitability for use in regulated markets and commitment to environmental safety standards.