S-91211A115 1/4"-20 x 1 1/4" ASME B18.2.1, SAE J429 High-Strength Grade 8 Steel Thread-Locking Hex Head Screws

Key Features & Benefits at a Glance

• Exceptional Load-Bearing Capability – With 150,000 psi tensile strength and Rockwell C33 hardness, this screw withstands extreme mechanical stresses, reducing failure risks in heavy-duty assemblies.
• Reliable Vibration Resistance – The integrated nylon patch thread locker prevents loosening under dynamic loads, maintaining clamp force in temperatures from -55° to 250°F.
• Corrosion-Resistant Coating – Zinc yellow-chromate plating on steel provides enhanced protection against rust and chemical exposure, extending service life in harsh environments.
• Precision Thread Engagement – Class 2A thread fit with UNC coarse threading ensures easy installation and consistent torque performance, minimizing cross-threading issues.
• Optimized for High-Strength Applications – Meets Grade 8 standards and ASME B18.2.1/SAE J429 specifications, guaranteeing compliance with industrial reliability requirements.
• Secure Partial Threading Design – The unthreaded shank section increases shear strength and alignment stability, ideal for structured joint assemblies.
• Versatile External Hex Drive – Standard 7/16" hex head allows for high-torque application with common tools, speeding up installation in confined spaces.

Professional Applications & Engineering Value

Engineered for demanding industrial settings, this Grade 8 hex head screw combines zinc yellow-chromate plated steel construction with a nylon patch locking mechanism to address critical challenges like vibration-induced loosening and environmental degradation. The 1/4"-20 UNC coarse thread and partial threading enhance grip in metals and composites, while the external hex drive supports efficient mounting in machinery, automotive frames, and structural steelwork. By maintaining integrity under 150,000 psi tensile loads and wide temperature swings, it reduces maintenance frequency and ensures long-term joint security in heavy-duty fastening applications.

Specification Summary & Compliance

This fastener adheres to Class 2A thread fit tolerances and UNC coarse thread standards, with manufacturing conforming to ASME B18.2.1 and SAE J429 specifications. The zinc yellow-chromate plating meets RoHS and REACH environmental directives, ensuring safe use in regulated industries. Dimensions include a 1 1/4" length, 1/4"-20 thread size, and 7/16" head width, providing precise compatibility with standard components.