S-91257A172 1/2"-20 x 4 1/4" ASME B18.2.1, SAE J429 High-Strength Grade 8 Steel Hex Head Screws

Key Features & Benefits at a Glance

• Exceptional tensile strength of 150,000 psi ensures reliable performance in high-stress applications, preventing fastener failure.
• Superior corrosion resistance from zinc yellow-chromate plating protects against harsh industrial environments, extending service life.
• High hardness rating (Rockwell C33) provides excellent wear resistance and durability under heavy loads.
• Fine UNF thread design offers improved vibration resistance and more precise tension control compared to coarse threads.
• Class 2A thread fit ensures easy assembly and consistent performance while maintaining secure fastening.
• Partially threaded shank allows for optimal clamp load distribution and prevents thread damage during installation.
• External hex drive design enables high-torque installation with standard tools for efficient assembly and maintenance.

Professional Applications & Engineering Value

Engineered for heavy-duty industrial applications, these Grade 8 hex head screws deliver exceptional performance where reliability is critical. The combination of 150,000 psi tensile strength and Rockwell C33 hardness makes them ideal for structural connections, machinery assembly, and equipment manufacturing that demand maximum load-bearing capacity. The zinc yellow-chromate plating provides superior protection against corrosion in challenging environments including outdoor installations, manufacturing facilities, and automotive applications. The 1/2"-20 UNF fine thread configuration ensures secure fastening in materials where vibration resistance is essential, while the partially threaded design concentrates clamping force precisely where needed. These industrial hex bolts solve common engineering challenges by offering a balanced combination of strength, corrosion resistance, and installation efficiency.

Specification Summary & Compliance

This 4 1/4" length hex head screw features Class 2A thread fit for standard tolerance applications and UNF fine threading with precise dimensional accuracy. The fastener complies with ASME B18.2.1 and SAE J429 Grade 8 specifications, ensuring consistent quality and performance. Manufacturing follows industry standards for dimensional requirements, mechanical properties, and material composition. The product meets relevant industry regulations for heavy-duty fastening applications requiring verified mechanical properties and reliable performance characteristics.