S-91253A303 1/4"-28 x 1/2" ASTM F835 Alloy Steel Hex Drive Flat Head Screws

Key Features & Benefits at a Glance

• Exceptional load-bearing capability with 130,000 psi tensile strength and Rockwell C39 hardness for reliable performance in demanding applications
• Precise Class 3A thread fit ensures superior engagement and vibration resistance in fine-threaded assemblies
• Corrosion-resistant black-oxide finish on alloy steel provides enhanced durability in industrial environments
• Efficient hex drive design (5/32") allows for secure installation and high torque application without cam-out
• Optimized 82° countersink angle enables flush mounting for clean, professional finishes in precision applications
• Fully threaded construction delivers maximum holding power along the entire fastener length
• Right-hand UNF fine threading provides superior resistance to loosening under vibration compared to coarse threads

Professional Applications & Engineering Value

Engineered for high-performance industrial applications, these black-oxide alloy steel flat head screws solve critical fastening challenges where vibration resistance and precise flush mounting are essential. The Class 3A UNF fine threads maintain tight tolerances in machinery, automotive components, and precision equipment, preventing loosening under dynamic loads. The 82° countersink angle and flat head profile create seamless surfaces in countersunk holes, eliminating protrusions that could interfere with moving parts. With 130,000 psi tensile strength, these hex drive screws withstand extreme mechanical stresses while the black-oxide surface treatment provides corrosion protection in demanding environments, making them ideal for manufacturing equipment, aerospace assemblies, and heavy-duty machinery requiring reliable, long-term fastening solutions.

Specification Summary & Compliance

Manufactured to exacting Class 3A thread fit tolerances with UNF (Unified National Fine) 1/4"-28 thread specification. Complies with ASME B18.3 and ASTM F835 manufacturing standards for dimensional accuracy and mechanical properties. Meets environmental regulations including RoHS 3 (2015/863/EU) compliance and REACH (EC 1907/2006) requirements, ensuring safe use in regulated industries. Features right-hand threading and fully threaded design for consistent performance across industrial applications.