Osg 0144201 Extension Tap 1/4-28 Unf 3 Flute H3

Product Description

The OSG 0144201 is a spiral flute extension tap designed for threading operations in ferrous and stainless steel materials. Built from vanadium high-speed steel with a steam oxide finish, it handles bottoming applications where threads must be cut close to the bottom of a blind hole. The tap runs a 1/4-28 UNF thread form to a 3B class of fit with an H3 thread limit. Its 6-inch overall length provides the reach needed for deep or obstructed workpieces where a standard-length tap cannot access the thread zone. Three flutes with a 30-degree right-hand helix promote chip evacuation and help maintain consistent thread form at depth.

This extension tap is suited for machine shop, maintenance, and production threading work on hardened steel, low-carbon steel, medium-carbon steel, and stainless steel. The reduced shank and extended neck allow use in confined setups or fixtures where clearance is limited. It is appropriate for CNC tapping, drill press, or tapping arm applications where controlled feed and speed can be maintained. Series 398 designates this as part of OSG's extension tap line for precision threading with fine unified thread forms.

Key Features

• 1/4-28 UNF right-hand thread, 3B class of fit with H3 thread limit for consistent tolerance control
• Spiral flute bottoming chamfer cuts threads to the bottom of blind holes
• Vanadium high-speed steel construction for durability in hardened and stainless steel applications
• Steam oxide finish reduces friction and improves lubrication retention during tapping
• 6-inch overall length with 1.496-inch neck provides extended reach in deep or obstructed workpieces
• Reduced shank with 0.255-inch shank diameter and 0.191-inch square for standard tap holders

Compatibility

Compatible material applications include hardened steel, low-carbon steel, medium-carbon steel, and stainless steel. Designed for use in standard tap holders accepting a 0.255-inch shank diameter and 0.191-inch square drive.

Installation Notes

Installation is performed by machinists or maintenance technicians using a tapping arm, drill press, or CNC machine with tapping capability. Power down and secure the workpiece before tool changes. Use appropriate cutting fluid for the material being tapped, particularly with stainless steel. Do not exceed the recommended surface feet per minute for high-speed steel tooling in the material being threaded.