S-91211A121 1/4"-20 x 1 3/4" ASME B18.2.1, SAE J429 High-Strength Grade 8 Steel Thread-Locking Hex Head Screws

Key Features & Benefits at a Glance

• Vibration-resistant locking: Permanent Nylon Patch thread locker ensures secure fastening even under extreme vibration, eliminating the need for separate locking washers.
• Exceptional strength for heavy loads: Grade 8 classification and 150,000 psi tensile strength provide superior reliability in high-stress applications.
• Durable corrosion protection: Zinc Yellow-Chromate plating on steel offers excellent resistance to rust and corrosion, extending the fastener's service life.
• Wide operational temperature range: Performs reliably in environments from -55°F to 250°F, making it suitable for diverse industrial settings.
• Optimized for high-torque assembly: The external hex head design allows for easy installation and removal with standard tools, improving assembly efficiency.
• Secure thread engagement: Class 2A thread fit on the 1/4"-20 UNC coarse thread ensures consistent, reliable mating with nuts and tapped holes.
• Proven industry compliance: Manufactured to meet ASME B18.2.1 and SAE J429 specifications, guaranteeing dimensional accuracy and performance.

Professional Applications & Engineering Value

This Grade 8 Hex Head Screw is engineered to solve critical challenges in heavy machinery, automotive, and construction equipment where vibration resistance and joint integrity are paramount. The Nylon Patch thread locker is permanently applied, creating a prevailing torque that prevents loosening under dynamic loads, a common failure point in industrial applications. The Zinc Yellow-Chromate plated steel construction provides a robust barrier against corrosion, essential for equipment operating in harsh or outdoor environments. With its 150,000 psi tensile strength and Rockwell C33 hardness, this heavy-duty fastener maintains clamp load in high-stress assemblies, ensuring long-term structural stability and reducing maintenance downtime. The 1/4"-20 UNC coarse thread and partial threading offer optimal grip and shear strength, making it a reliable choice for critical connections.

Specification Summary & Compliance

This screw features a 1/4"-20 UNC thread with a Class 2A fit, ensuring precise and consistent thread engagement. It is manufactured in compliance with ASME B18.2.1 and SAE J429 standards, confirming its dimensional accuracy and mechanical properties. The product is also REACH (EC 1907/2006) compliant, adhering to environmental and safety regulations for hazardous substances. The specified Rockwell C33 hardness and 150,000 psi tensile strength are certified per the Grade 8 classification.