Osg 1295300 Extension Tap 3/8-16 Unc H3 Spiral Point

Product Description

The OSG 1295300 is a spiral point plug extension tap designed for threading 3/8-16 UNC internal threads in deep or hard-to-reach bores where standard-length taps cannot reach. Built from high-speed steel with a bright uncoated finish, this tap measures 6 inches overall length with a 1-1/4 inch thread length and a reduced shank for extended reach clearance. The spiral point geometry pushes chips ahead of the cutting flutes, making it suitable for through-hole threading operations. With an H3 thread limit and Class 3B fit, it produces tight-tolerance threads appropriate for precision fastening applications. Licensed machinists, toolmakers, and maintenance technicians are the primary users.

This extension tap is rated for threading aluminum, carbon steel, cast iron, and hardened steel. The plug chamfer style allows the tap to start easily and is suited for through holes where the full thread form is required before the bottom of the bore. The 6-inch overall length provides the reach needed for fixtures, deep housings, manifolds, and structural weldments where a standard tap wrench or short-shank tap cannot access the workpiece. It is commonly used in machine shops, fabrication facilities, and field maintenance environments.

Key Features

• Spiral point geometry pushes chips forward, ideal for through-hole threading
• H3 thread limit with Class 3B fit for tight-tolerance thread production
• 6-inch overall length with reduced shank for deep or obstructed bore access
• High-speed steel construction handles aluminum, carbon steel, cast iron, and hardened steel
• Plug chamfer for standard through-hole starting and full thread engagement
• Bright uncoated finish suitable for use with cutting fluids across a range of materials

Compatibility

Designed for use in standard 3/8-16 UNC through-hole threading applications in aluminum, carbon steel, cast iron, and hardened steel workpieces. Compatible with standard tap handles and extension tap holders sized for a 0.381-inch shank diameter.

Installation Notes

Secure the workpiece fully before tapping and ensure the pilot hole diameter is correct for 3/8-16 UNC threads before starting. Use an appropriate cutting fluid or tapping compound matched to the workpiece material to extend tool life and improve thread finish. Apply steady, even torque and back the tap off periodically to break chips and prevent binding. Replace the tap if cutting resistance increases significantly, as forcing a worn tap in hardened materials risks breakage and workpiece damage.