S-91257A422 1/4"-28 x 5 1/2" ASME B18.2.1, SAE J429 High-Strength Grade 8 Steel Hex Head Screws

Key Features & Benefits at a Glance

• Exceptional Strength & Reliability: Grade 8 classification and 150,000 psi tensile strength ensure maximum load-bearing capacity and resistance to failure in high-stress applications.
• Superior Corrosion Protection: Zinc yellow-chromate plating provides a robust barrier against rust and environmental degradation, extending the service life of components.
• Precision Thread Fit: Class 2A UNF fine threads offer excellent vibration resistance and secure fastening, reducing the risk of loosening in dynamic environments.
• Optimized for Heavy-Duty Use: Rockwell C33 hardness provides excellent wear resistance, maintaining integrity under repeated stress and impact.
• Industry Standard Compliance: Manufactured to ASME B18.2.1 and SAE J429 specifications, guaranteeing consistent quality, dimensional accuracy, and interchangeability.
• Secure & Efficient Installation: The external hex drive and hex head design allow for high-torque application with standard tools, ensuring a tight, reliable fit.
• Versatile Partial Threading: The partially threaded design allows for a strong, unthreaded shank to bear shear loads while the threaded portion provides secure clamping force.

Professional Applications & Engineering Value

This Grade 8 hex head screw is engineered to solve critical challenges in demanding industrial environments. Its high tensile strength and Rockwell C33 hardness make it ideal for heavy machinery, construction equipment, and automotive assemblies where structural integrity is non-negotiable. The UNF fine thread and Class 2A fit provide superior resistance to vibrational loosening, a common failure point in dynamic systems. The zinc yellow-chromate plating offers a vital layer of corrosion resistance, protecting investments in harsh or outdoor settings. By combining a partially threaded design with an external hex drive, this fastener delivers optimal clamping force and ease of installation, making it a reliable choice for engineers specifying components for high-performance, long-lasting assemblies.

Specification Summary & Compliance

This fastener adheres to strict dimensional and performance standards, including a Class 2A thread fit for precision and a UNF (Unified National Fine) thread form. It is manufactured in compliance with ASME B18.2.1 and SAE J429 specifications, ensuring consistent quality and reliability. The product meets common industry requirements for material and performance, providing assurance for professional procurement and application.