S-91253A108 4-40 x 3/8" ASTM F835 Alloy Steel Hex Drive Flat Head Screws

Key Features & Benefits at a Glance

• Exceptional tensile strength of 130,000 PSI for reliable load-bearing in demanding industrial environments
• Superior corrosion resistance with Black-Oxide finish, extending service life in harsh conditions
• Precise Class 3A thread fit ensures tight, secure fastening with minimal risk of loosening
• 82° countersink angle allows for flush mounting, reducing snagging and improving aesthetics
• Hex drive design provides superior torque transmission and prevents cam-out during installation
• Fully threaded construction offers maximum grip length and uniform stress distribution
• High hardness rating (Rockwell C39) maintains thread integrity under repeated use

Professional Applications & Engineering Value

These 4-40 UNC flat head screws deliver critical performance advantages in precision assembly applications. The Black-Oxide Alloy Steel construction provides excellent corrosion protection while maintaining the 130,000 PSI tensile strength required for high-stress applications. The coarse UNC thread design ensures rapid installation and superior resistance to vibration loosening in machinery, electronics, and automotive assemblies. The combination of Class 3A thread fit and 82° countersink angle creates reliable, flush-mounted connections that withstand thermal cycling and mechanical shock. These fully threaded hex drive screws are engineered to solve common industrial fastening challenges including stripped heads, corrosion failure, and installation inefficiency.

Specification Summary & Compliance

Manufactured to Class 3A thread fit tolerances with 4-40 UNC coarse threads and right-hand threading. Compliant with ASME B18.3 and ASTM F835 specifications for dimensional accuracy and mechanical properties. Meets environmental standards including RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) compliance for restricted substance control.