S-90585A203 4-40 x 5/16" ASME B18.3 Stainless Steel Hex Drive Flat Head Screws

Key Features & Benefits at a Glance

• Superior corrosion resistance from 316 Stainless Steel and passivated finish, ideal for harsh marine and chemical environments.
• Exceptional mechanical strength with a 70,000 psi tensile strength and Rockwell B55 hardness for reliable, long-term fastening.
• Precise, secure fit due to the Class 3A thread fit and UNC coarse thread, reducing the risk of cross-threading and loosening.
• Efficient installation and removal with the 1/16" hex drive, providing a positive grip for high-torque applications.
• Flush, low-profile seating with the standard 82° flat head, ideal for applications where a smooth surface is critical.
• Full thread engagement along the 5/16" length for maximum grip and load distribution in thin materials.
• Guaranteed quality and safety through compliance with ASME B18.3, RoHS 3, and REACH regulations.

Professional Applications & Engineering Value

This 4-40 UNC flat head screw is engineered to solve critical fastening challenges in demanding sectors. The core value lies in its 316 Stainless Steel construction, which provides exceptional resistance to chlorides and acidic agents, making it a top choice for marine hardware, chemical processing equipment, and food-grade machinery. The combination of a passivated finish and Rockwell B55 hardness ensures the screw withstands abrasive environments and repeated disassembly without galling or significant wear. The coarse UNC thread and Class 3A fit offer superior vibration resistance, preventing spontaneous loosening in dynamic assemblies. Its fully threaded design and flat head profile allow for a secure, flush mount in countersunk holes, which is essential for maintaining aerodynamic surfaces on enclosures or ensuring operator safety on machinery.

Specification Summary & Compliance

This fastener adheres to strict dimensional and performance standards. The thread is manufactured to a precision Class 3A fit under the UNC (Unified National Coarse) standard. All physical dimensions, including the head profile and drive size, conform to the ASME B18.3 specification. The product is fully compliant with RoHS 3 (2015/863/EU) and REACH (EC 1907/2006), ensuring it is free from hazardous substances and safe for use in regulated markets.