Osg 1764901 Extension Tap 1/4-20 Spiral Point Plug

Product Description

The OSG 1764901 is a spiral point plug extension tap designed for threading operations in ferrous and stainless steel workpieces. Built from vanadium high-speed steel with a steam oxide finish, it offers improved lubricity and corrosion resistance during cutting. The tap cuts a 1/4-20 UNC right-hand thread to a 3B class of fit, making it suitable for precision threaded assemblies. With an overall length of 4 inches and a neck length of 1.5 inches, it provides the reach needed for recessed or deep-pocket tapping applications. A 3-flute spiral point design pushes chips ahead of the cut, reducing clogging in through-hole work. Machinists, toolroom technicians, and maintenance mechanics install this tap in manual tap handles or CNC tapping operations.

This extension tap is suited for threading carbon steel, hardened steel, and stainless steel in both production and maintenance environments. The reduced shank and extended neck length make it effective where standard-length taps cannot reach, such as counterbored holes, deep bosses, or fixtures with obstructed access. It belongs to the OSG Series 397 and carries a plug chamfer, which provides a gradual lead-in over several threads for easier starting in through-hole applications.

Key Features

• Spiral point plug geometry pushes chips forward, suited for through-hole tapping
• Vanadium high-speed steel construction handles carbon steel, hardened steel, and stainless steel
• Steam oxide finish reduces friction and provides light corrosion protection
• Extended neck length of 1.5 inches gives reach into deep or obstructed hole locations
• Reduced shank at 0.255 inches diameter accommodates standard tap holders
• H3 thread limit holds tight tolerances for 3B class of fit threaded connections

Compatibility

Designed for use in standard tap handles and CNC tapping heads that accept a 0.255-inch shank diameter. Rated for threading carbon steel, hardened steel, and stainless steel workpieces per the manufacturer material application data.

Installation Notes

This tap is installed by machinists or maintenance technicians using a tap wrench, tapping stand, or CNC machine with synchronized feed. Ensure the workpiece is securely fixtured and the pilot hole is drilled to the correct tap drill size for 1/4-20 UNC before starting. Apply appropriate cutting fluid for the workpiece material to extend tool life and improve thread quality. Inspect the tap for chipping or wear before each use and never force a tap that has stopped rotating, as tap breakage in blind holes is difficult to recover from.