S-91257A423 1/4"-28 x 6" ASME B18.2.1, SAE J429 High-Strength Grade 8 Steel Hex Head Screws

Key Features & Benefits at a Glance

• Maximum load-bearing capacity with Grade 8 classification and 150,000 psi tensile strength for critical structural applications
• Enhanced corrosion protection through zinc yellow-chromate plating, extending service life in harsh industrial environments
• Superior thread engagement with UNF fine threading and Class 2A fit ensuring vibration resistance and precise assembly
• Optimized torque transmission via external hex drive design that prevents tool slippage during high-tension installations
• Controlled thread distribution through partial threading that concentrates strength where needed while reducing weight
• Industry-standard compliance with ASME B18.2.1 and SAE J429 specifications for guaranteed interchangeability and reliability
• Rockwell C33 hardness rating providing exceptional wear resistance against repeated stress and abrasion

Professional Applications & Engineering Value

These Grade 8 hex head screws deliver critical performance in heavy machinery, structural steel connections, and high-vibration equipment where failure is not an option. The UNF fine thread configuration maintains clamping force under dynamic loads, while the zinc yellow-chromate plating creates a sacrificial barrier against chemical exposure and atmospheric corrosion. Engineers specify these partially threaded fasteners for applications requiring precise grip length control, as the unthreaded shank section provides enhanced shear strength. The external hex drive accommodates high-torque installation tools commonly used in industrial maintenance and manufacturing operations, ensuring consistent preload in critical joints.

Specification Summary & Compliance

Manufactured to ASME B18.2.1 dimensional standards and SAE J429 material specifications, these hex head screws feature Class 2A thread fit tolerances for consistent assembly performance. The 1/4"-28 UNF fine thread maintains precise pitch control across the 3/4" minimum thread length, while the 6" overall length with partial threading provides optimal strength-to-weight ratio. Compliant with RoHS and REACH environmental directives, these industrial fasteners meet rigorous quality assurance standards for material traceability and performance verification.