Osg 1769201 Extension Tap 1/2-20 Unf Spiral Flute

Product Description

The OSG 1769201 is a spiral flute extension tap designed for threading 1/2-20 UNF internal threads in applications where standard-length taps cannot reach. Built from vanadium high-speed steel with a steam oxide finish, this tap delivers controlled chip evacuation upward out of the hole, making it well suited for blind-hole threading operations. The modified bottoming chamfer allows thread cutting close to the bottom of a hole. With an overall length of 6 inches and a reduced shank, this tap extends reach in deep or obstructed bores. It is used by machinists and maintenance trades requiring precise 3B class-of-fit threads in ferrous materials.

This extension tap is intended for threading operations in carbon steel, hardened steel, and stainless steel workpieces. The 30-degree helix angle promotes smooth cutting and reliable chip removal in through and blind hole applications. The reduced shank and extended neck length of 1.933 inches allow access in recessed or hard-to-reach locations. This tap belongs to OSG Series 398 and is packaged individually for single-unit procurement.

Key Features

• Thread size 1/2-20 UNF with H3 thread limit for consistent 3B class-of-fit tolerances
• Spiral flute design with 30-degree helix angle for upward chip evacuation in blind holes
• Modified bottoming chamfer enables threading close to the bottom of a blind bore
• Vanadium high-speed steel construction rated for carbon steel, hardened steel, and stainless steel
• Steam oxide finish reduces friction and provides corrosion resistance during cutting
• Reduced shank and 6-inch overall length for extended reach in deep or obstructed bores

Compatibility

Designed for 1/2-20 UNF internal threading in carbon steel, hardened steel, and stainless steel. Suitable for use with standard tap holders and extensions accepting a 0.367-inch diameter reduced shank.

Installation Notes

This tap is installed and driven by a qualified machinist or tooling professional using a compatible tap wrench, tapping head, or CNC machine holder. Ensure the workpiece is securely fixtured and the spindle is aligned before engaging the tap. Always use appropriate cutting fluid for the workpiece material to extend tool life and maintain thread quality. Inspect the tap for wear or chipping before each use; a damaged tap can destroy threads or break inside the workpiece.