S-91259A431 5/16"-18 ASME B18.3, ASTM A108 Shoulder Screws

Key Features & Benefits at a Glance

• Exceptional load-bearing capacity with 140,000 psi tensile strength for reliable performance in high-stress assemblies.
• Superior corrosion resistance from the black oxide finish, extending service life in demanding industrial environments.
• Precise alignment and secure positioning ensured by the Class 3A thread fit and standard shoulder fit, minimizing assembly play.
• High torque application capability with the hex socket drive and knurled head, providing a secure grip and reducing tool slippage.
• Durable, long-lasting construction from alloy steel with Rockwell C32 hardness, resisting wear and deformation.
• Broad compatibility with 5/16"-18 UNC coarse threads, suitable for a wide range of industrial fastening applications.
• Regulatory peace of mind by meeting ASME B18.3 standards and being RoHS 3 and REACH compliant for global use.

Professional Applications & Engineering Value

This alloy steel shoulder screw is engineered to address critical challenges in precision machinery, automation systems, and heavy-duty equipment. The black oxide finish provides a robust barrier against rust and corrosion, essential for operations in humid or chemically aggressive environments. Its 5/16"-18 UNC coarse thread and Class 3A fit ensure tight, reliable fastening with minimal risk of loosening under vibration, making it ideal for securing rotating components, linkages, and bearings. The knurled head and hex socket drive allow for high-torque installation without stripping, while the precise shoulder diameter acts as a pivot or spacer, maintaining exact alignment in assemblies. This combination of material strength, precise tolerances, and protective coating delivers long-term reliability, reducing maintenance needs and downtime in industrial applications.

Specification Summary & Compliance

This shoulder screw adheres to strict dimensional standards, including a Class 3A thread fit for superior accuracy and a shoulder diameter tolerance of -0.004" to -0.002". It conforms to ASME B18.3 specifications and is manufactured from alloy steel per ASTM A108. The product is fully compliant with RoHS 3 (2015/863/EU) and REACH (EC 1907/2006) regulations, ensuring it meets global environmental and safety requirements for industrial use.