S-91211A142 5/16"-18 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

• Exceptional vibration resistance with a permanent nylon patch thread locker that maintains locking performance from -55°F to 250°F, preventing loosening in dynamic environments.
• Superior strength for demanding applications thanks to Grade 8 classification, offering a high tensile strength of 150,000 PSI to withstand extreme loads.
• Enhanced durability and corrosion resistance from the zinc yellow-chromate plated steel, providing a protective barrier against harsh industrial conditions.
• Reliable and easy installation with a standard external hex drive and coarse UNC threading, ensuring quick assembly and a secure Class 2A thread fit.
• Optimized for high-stress scenarios with a Rockwell C33 hardness, offering excellent wear resistance and structural integrity under pressure.
• Versatile partial threading design that allows for precise clamping force distribution, ideal for components requiring unthreaded shank sections.

Professional Applications & Engineering Value

This Grade 8 hex head screw is engineered to solve critical challenges in heavy machinery, automotive assemblies, and structural frameworks where vibration and high tensile loads are prevalent. The nylon patch thread locker is chemically bonded to the threads, creating a permanent locking feature that eliminates the need for separate washers or adhesives, reducing assembly time and maintenance. Manufactured from zinc yellow-chromate plated steel, it provides robust corrosion protection, extending service life in outdoor or chemically exposed environments. The coarse UNC thread and Class 2A fit ensure consistent engagement and ease of use in field repairs, while the partial threading offers flexibility in applications requiring shear strength along the shank. Ideal for construction equipment, truck chassis, and industrial presses, this fastener delivers reliable performance where failure is not an option.

Specification Summary & Compliance

This screw adheres to Class 2A thread fit tolerances for consistent assembly and meets ASME B18.2.1 and SAE J429 specifications, ensuring dimensional accuracy and material integrity. The UNC coarse thread (5/16"-18) and partial threading with a minimum thread length of 7/8" provide reliable fastening. Compliance with industry standards guarantees suitability for high-stress applications, with material and plating processes aligned to common industrial requirements for performance and safety.