Osg 1768301 Extension Tap 1/4-28 Spiral Flute Hss

Product Description

The OSG 1768301 is a spiral flute extension tap designed for threading 1/4-28 UNF right-hand threads in applications where standard-length taps cannot reach. Built from vanadium high-speed steel with a steam oxide finish, this tap handles carbon steel, hardened steel, and stainless steel. It features a modified bottoming chamfer, a 30-degree helix angle, and 3 flutes arranged for right-hand cutting. The H3 thread limit and 3B class of fit keep tolerances tight for precision threaded assemblies. At 6 inches overall length with a reduced shank and 1.5-inch neck, it provides the reach needed for deep or recessed hole work.

This tap is suited for production and maintenance threading where access depth is a constraint. The spiral flute design evacuates chips back toward the shank, making it effective in blind holes. Material application includes carbon steel, hardened steel, and stainless steel, covering a broad range of industrial and mechanical service work. Machinists, toolmakers, and maintenance technicians install this tap in CNC machining centers, manual mills, and tapping fixtures. The modified bottoming chamfer allows threading close to the bottom of a blind hole while the extended neck clears obstructions.

Key Features

• 1/4-28 UNF thread size with H3 thread limit and 3B class of fit for controlled tolerance
• Spiral flute geometry evacuates chips toward the shank, suitable for blind-hole threading
• Modified bottoming chamfer threads close to the bottom of blind holes
• 30-degree helix angle improves chip flow in stainless steel and hardened steel
• Steam oxide coating reduces friction and improves lubrication retention
• Reduced shank and 1.5-inch neck length provide clearance in deep or obstructed setups

Compatibility

Designed for threading 1/4-28 UNF right-hand blind and through holes in carbon steel, hardened steel, and stainless steel. Compatible with standard tap holders and tapping chucks sized for a 0.255-inch shank diameter.

Installation Notes

Install in a tapping chuck or rigid holder rated for the shank diameter and ensure the workpiece is securely fixtured before beginning the threading cycle. Apply appropriate cutting fluid for the work material, particularly when tapping stainless or hardened steel, to extend tool life and maintain thread quality. Power down or disengage the spindle before changing or inspecting the tap. Follow shop and manufacturer guidelines for speed and feed selection based on material and tap geometry.