S-90403A844 5/16"-18 x 3/4" ASME B18.13 Steel Pan Head Phillips Screws with Internal-Tooth Lock Washer

Key Features & Benefits at a Glance

• Enhanced Vibration Resistance with integrated internal-tooth lock washer prevents loosening under dynamic loads
• Superior Corrosion Protection through zinc-plated steel construction for extended service life in harsh environments
• Optimized Driving Efficiency with Phillips No. 4 drive for secure torque transmission and reduced cam-out risk
• Maximum Thread Engagement through fully threaded design ensures consistent clamping force across the entire length
• High Load-Bearing Capacity with 60,000 psi tensile strength and Rockwell B69 hardness for demanding applications
• Reliable Fastening Performance with Class 2A thread fit and UNC coarse threads for quick assembly and disassembly
• Secure Seating with standard pan head profile providing stable bearing surface and improved aesthetics

Professional Applications & Engineering Value

These zinc-plated steel rounded head screws deliver exceptional engineering value in industrial fastening scenarios where vibration resistance and corrosion protection are critical. The combination of internal-tooth lock washers and coarse UNC threads addresses common challenges in machinery assembly, electrical enclosures, and automotive components where constant movement and environmental exposure can compromise joint integrity. The fully threaded 5/16"-18 design ensures maximum thread contact throughout the 3/4" length, providing uniform stress distribution that prevents localized fatigue failure. With 60,000 psi tensile strength and Rockwell B69 hardness, these screws maintain clamping force under heavy loads while the zinc plating creates a sacrificial barrier against oxidation, making them ideal for outdoor equipment, manufacturing fixtures, and construction applications requiring durable, maintenance-free fastening solutions.

Specification Summary & Compliance

Manufactured to precise dimensional standards with Class 2A thread fit and UNC coarse threads (5/16"-18) ensuring consistent performance across industrial applications. Complies with ASME B18.13 specifications for mechanical fasteners and meets environmental regulations including RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) compliance. The screw features a standard pan head profile with 0.615" diameter and incorporates an internal-tooth lock washer (0.61" OD, 0.034" thickness) manufactured from zinc-plated steel for consistent locking performance.