S-91266A548 1/4"-20 x 1 3/4" ASTM F835 Alloy Steel Thread-Locking Hex Drive Flat Head Screws

Key Features & Benefits at a Glance

• Vibration-resistant locking: Integrated nylon patch thread locker prevents loosening under dynamic loads, maintaining clamp force in temperatures from -65°F to 250°F.
• Exceptional strength-to-weight ratio: Alloy steel construction with 130,000 psi tensile strength and Rockwell C39 hardness withstands high-stress applications without failure.
• Precision-engineered fit: Class 3A thread fit ensures tighter tolerances and superior engagement in tapped holes, reducing the risk of cross-threading.
• Optimized drive efficiency: 5/32" hex drive and flat head design allow for high-torque installation and a flush finish in countersunk applications.
• Enhanced corrosion protection: Black-oxide finish on alloy steel provides a durable barrier against oxidation in demanding industrial environments.
• Reliable coarse threading: 1/4"-20 UNC coarse threads enable faster installation and better performance in softer materials or where debris is present.
• Versatile partial threading: Partially threaded shank with 1" minimum thread length allows for precise clamping on specific material thicknesses.

Professional Applications & Engineering Value

This black-oxide alloy steel flat head hex screw is engineered to address critical challenges in industrial assembly and heavy-duty machinery. The combination of high tensile strength (130,000 psi) and a nylon patch thread locker ensures reliable performance in high-vibration environments, such as automotive components, electrical enclosures, and construction equipment. The UNC coarse thread facilitates quick installation and provides superior holding power in cast or brittle materials, while the flat head with 82° countersink angle delivers a seamless finish, reducing snag points and improving safety. Its partially threaded design allows engineers to target clamping force precisely, minimizing stress concentration and enhancing joint integrity. Ideal for applications requiring secure fastening and compliance with rigorous industry standards, this screw offers long-term durability and resistance to environmental factors.

Specification Summary & Compliance

This screw features a 1/4"-20 UNC coarse thread with Class 3A fit for precise thread engagement and a partially threaded shank with 1" minimum thread length. It is manufactured from alloy steel with a black-oxide finish and meets ASTM F835 specifications for mechanical properties and performance. The product is fully compliant with RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) regulations, ensuring it is free from hazardous substances and suitable for global industrial use.