Osg 1298300 Spiral Flute Extension Tap 1/4-28 Unf

Product Description

The OSG 1298300 is a spiral flute extension tap designed for threading 1/4-28 UNF holes in a wide range of metal workpieces. Built from high-speed steel with a bright, uncoated finish, this tap features a bottoming chamfer for threading close to the bottom of blind holes. The 50-degree helix angle drives chips up and out of the flute during the cut. At 6 inches overall length, the extended reach makes it suited for applications where a standard-length tap cannot access the work area. Three flutes and an H3 thread limit provide consistent thread tolerance control on production and repair work alike.

This tap is intended for use in aluminum, carbon steel, and cast iron. The bottoming chamfer allows full thread engagement near the base of a blind hole, making it appropriate for fastener bores with limited depth clearance. The reduced shank and 1-inch thread length support use in both CNC tapping cycles and hand-tapping setups where tool clearance is a factor. The 3B class of fit targets standard tolerance internal threads used across general mechanical assembly.

Key Features

• 1/4-28 UNF thread form with H3 thread limit for controlled tolerance
• Bottoming chamfer for threading to the bottom of blind holes
• 50-degree helix angle for efficient chip evacuation in spiral flute design
• 6 inches overall length provides extended reach into recessed bores
• High-speed steel construction suitable for aluminum, carbon steel, and cast iron
• Reduced shank with 0.255-inch shank diameter for compatibility with standard tap holders

Compatibility

Designed for use in standard tap holders and CNC tapping chucks that accept a 0.255-inch reduced shank. Suitable for threading 1/4-28 UNF internal threads in aluminum, carbon steel, and cast iron workpieces.

Installation Notes

Installation and use should be performed by a machinist or qualified tradesperson familiar with tapping operations. Always secure the workpiece and use the appropriate cutting fluid for the material being tapped. Ensure the tap driver or chuck is properly aligned to avoid tap breakage, especially near the bottom of blind holes. Follow applicable shop safety practices and machine manufacturer guidelines when operating tapping equipment.