Holo-krome 77478 Hex Socket Cap Screw 1/4-28 Unf

Product Description

The HOLO-KROME 77478 is a hex socket cap screw designed for high-strength fastening in precision mechanical assemblies. It features a 1/4-28 UNF thread size and a 3-inch length under head, with partial threading along the shank. Drive engagement is through a 3/16-inch hex socket. The alloy steel construction is finished with a black oxide coating that provides moderate corrosion resistance and reduces light reflection in service environments. This fastener meets ASME B18.3 and ASTM A574 standards, making it suitable for applications requiring controlled tensile strength and dimensional consistency.

This screw is commonly used in machine assembly, equipment maintenance, and mechanical fabrication where a recessed drive cap screw is required. Partial threading allows for precise clamping without thread engagement across the full grip length, which is important in joint assemblies with clearance holes. It is installed by HVAC technicians, millwrights, machinists, and field service professionals working on mechanical equipment requiring UNF fine-thread fasteners.

Key Features

• 1/4-28 UNF fine thread for precise thread engagement and secure clamping
• 3-inch length under head with partial threading for clearance-hole joint applications
• 3/16-inch hex socket drive for use with standard Allen keys or hex bits
• Alloy steel construction meets ASTM A574 high-strength socket screw requirements
• Black oxide finish provides mild corrosion resistance and low-glare surface
• Conforms to ASME B18.3 dimensional standards

Compatibility

Designed as a standard ASME B18.3 hex socket cap screw suitable for mechanical assemblies requiring a 1/4-28 UNF fine-thread partially threaded cap screw with a 3/16-inch hex drive.

Installation Notes

Installation requires a 3/16-inch hex key or socket bit driver. Ensure mating threads are clean and free of debris before installation. De-energize and lock out any equipment before fastener service or replacement. Torque to the value specified by the equipment manufacturer for 1/4-28 alloy steel fasteners in the application.