Osg 0143701 Extension Tap 4-40 Unc 3 Flute Spiral Flute

Product Description

The OSG 0143701 is a spiral flute extension tap designed for threading 4-40 UNC holes in a wide range of metals. Built from vanadium high-speed steel (VHSS) with a steam oxide finish, it delivers durability and reduced friction during cutting. The bottoming chamfer allows threading close to the bottom of blind holes. At 6 inches overall length, it reaches into recessed or deep cavities where standard-length taps cannot. The 30-degree helix angle promotes chip evacuation in through and blind hole applications, making it well suited for production and maintenance threading work. Licensed machinists and toolroom professionals are the typical end users for this tap.

This tap is intended for threading operations in hardened steel, low-carbon steel, medium-carbon steel, and stainless steel. The extension length makes it practical for deep-reach applications on CNC machining centers, drill presses, and manual tapping setups where standard tap length is insufficient. The H2 thread limit provides a controlled fit range for 2B and 3B class-of-fit threads, which are the most common tolerances in general mechanical assembly and industrial fastener applications.

Key Features

• 4-40 UNC thread form with H2 thread limit for 2B and 3B class-of-fit tolerances
• Spiral flute design promotes chip evacuation in blind and through holes
• Bottoming chamfer allows threading to near the bottom of blind holes
• Vanadium high-speed steel construction for wear resistance in ferrous and stainless materials
• Steam oxide finish reduces friction and provides mild corrosion resistance during use
• 6 inch overall length with reduced shank for deep-reach threading access

Compatibility

Designed for use in hardened steel, low-carbon steel, medium-carbon steel, and stainless steel workpieces requiring 4-40 UNC threads. Suitable for use with standard tap wrenches and machine tap holders that accept the 0.141 inch shank diameter.

Installation Notes

Threading operations should be performed by a qualified machinist following standard tapping procedures. Secure the workpiece firmly before tapping and use a cutting fluid appropriate for the workpiece material to extend tool life and improve thread finish. When using in a machine setup, verify spindle speed is appropriate for the material and tap diameter before starting the cut. Inspect the tap for wear or chipping before each use, as a damaged cutting edge can cause tap breakage or out-of-tolerance threads.