S-91251A304 3/4"-16 x 5 1/2" ASTM A574 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 in critical applications.
• Superior corrosion resistance from the black-oxide finish extends service life and maintains integrity in harsh industrial environments.
• Precise Class 3A thread fit provides tighter tolerances for secure, vibration-resistant assemblies, minimizing loosening over time.
• High hardness rating (Rockwell C37) offers excellent wear resistance, maintaining thread integrity through repeated use and installation.
• UNRF fine threading delivers improved clamping force distribution and better sealing capabilities compared to coarse threads.
• Partially threaded design allows for optimal grip length control, preventing thread damage in non-threaded sections and simplifying alignment.
• 5/8" hex drive compatibility enables high-torque installation with standard tools, reducing assembly time and improving workplace efficiency.

Professional Applications & Engineering Value

These Black-Oxide Alloy Steel Socket Head Cap Screws are engineered to address common industrial challenges where vibration resistance, corrosion protection, and high tensile strength are paramount. The UNRF fine thread configuration provides superior load distribution in precision machinery, automotive assemblies, and heavy equipment applications where Class 3A fit ensures minimal backlash and reliable performance. The black-oxide surface treatment creates a protective barrier against oxidation and chemical exposure, making these socket head cap screws ideal for outdoor equipment, manufacturing fixtures, and aerospace components. With their partially threaded design, they eliminate unnecessary thread engagement points, reducing stress concentration and preventing cross-threading in blind holes. The combination of 170,000 psi tensile strength and Rockwell C37 hardness ensures these fasteners maintain clamping force under extreme dynamic loads, making them suitable for high-vibration environments and critical structural connections.

Specification Summary & Compliance

These inch-system fasteners feature precision 3/4"-16 UNRF fine threads with Class 3A fit tolerance for superior thread engagement. Manufacturing complies with ASTM A574 specification for alloy steel socket head cap screws, ensuring consistent quality and performance. The products are fully compliant with RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) regulations, meeting international environmental and safety standards for industrial applications.