S-91255A108 4-40 x 3/8" ASTM F835 Steel Button Head Hex-Drive Screws

Key Features & Benefits at a Glance

• Exceptional corrosion resistance with black-oxide coating, extending service life in demanding industrial environments
• Superior torque transmission through hex drive design, preventing stripping and ensuring secure installation
• High tensile strength of 120,000 psi provides reliable fastening integrity under substantial mechanical stress
• Precision Class 3A thread fit ensures consistent engagement and vibration resistance in critical assemblies
• Rockwell C39 hardness rating maintains structural integrity and wear resistance through repeated use cycles
• Coarse UNC threading enables rapid installation and superior holding power in various materials
• Full compliance with industry standards including ASME B18.3 and ASTM F835 for guaranteed performance consistency

Professional Applications & Engineering Value

These 4-40 UNC thread screws with black-oxide alloy steel construction address critical engineering challenges in industrial fastening applications. The rounded head design with hex drive provides optimal torque application while minimizing surface protrusion, making them ideal for machinery, electronic enclosures, and precision equipment where flush mounting is essential. The Class 3A thread fit ensures precise engagement in tapped holes, reducing the risk of cross-threading and providing consistent clamping force. The combination of 120,000 psi tensile strength and Rockwell C39 hardness delivers exceptional durability in high-vibration environments, while the black-oxide surface treatment provides reliable corrosion protection without dimensional interference, maintaining the coarse thread geometry for superior pull-out resistance in various substrate materials.

Specification Summary & Compliance

These precision rounded head screws feature 4-40 UNC coarse threads with Class 3A fit for superior dimensional accuracy and consistent performance. Manufacturing complies with ASME B18.3 and ASTM F835 specifications, ensuring standardized quality and interchangeability. Environmental compliance includes RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) regulations, confirming they are free from restricted substances and suitable for global industrial applications requiring stringent environmental standards.