Osg 1296000 Extension Tap 4-40 Unc Hss Spiral Flute

Product Description

The OSG 1296000 is a spiral flute extension tap designed for threading operations in confined or deep-reach applications where a standard-length tap cannot access the workpiece. Built from high-speed steel with a bright uncoated finish, this right-hand tap produces 4-40 UNC internal threads with a plug chamfer entry. The 2-flute spiral flute geometry evacuates chips up and out of the hole, making it well suited for blind hole threading. At 4 inches overall length with a 9/16-inch thread length and H2 thread limit, it delivers controlled tolerance for 2B and 3B class of fit applications.

This tap is intended for use on aluminum, carbon steel, and cast iron workpieces. The extended overall length allows machinists, tool and die makers, and maintenance technicians to reach threads in recessed bores, deep counterbores, or assemblies where standard-reach tooling is not practical. The reduced shank and 50-degree helix angle support chip flow in both CNC tapping cycles and hand-tapping setups. It is suited for low-volume production and repair threading in job shop, maintenance, and light manufacturing environments.

Key Features

• Spiral flute geometry with 50-degree helix angle evacuates chips upward out of blind holes
• 4-inch overall length provides extended reach for deep or recessed threading applications
• H2 thread limit maintains controlled tolerance for 2B and 3B class of fit
• Plug chamfer entry eases tap start and distributes cutting load across multiple threads
• Reduced shank design allows use in standard tap holders and collets
• High-speed steel construction handles aluminum, carbon steel, and cast iron without coating

Compatibility

Designed for threading 4-40 UNC right-hand internal threads in aluminum, carbon steel, and cast iron. Compatible with standard tap holders and collets accepting a 0.141-inch shank diameter. Suitable for 2B and 3B class of fit thread requirements per OSG Series 918.

Installation Notes

Power down or disengage the spindle before loading or removing the tap. Use appropriate cutting fluid for the workpiece material to reduce heat buildup and extend tool life. Ensure the tap holder provides adequate axial float when used in CNC tapping cycles to prevent thread distortion. Inspect the tap for wear or chipping before each use, as a damaged cutting edge on a small-diameter tap can cause breakage and part rejection.