Osg 1768701 Spiral Flute Extension Tap 3/8-16 Unc

Product Description

The OSG 1768701 is a spiral flute extension tap designed for threading 3/8-16 UNC 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 ejection through its 30-degree right-hand helix and three-flute geometry. The modified bottoming chamfer allows threading closer to the bottom of blind holes than a standard plug or taper chamfer. At 6 inches overall length with a 1.875-inch neck, it provides the reach needed for recessed or deep-pocket threading operations. Shank diameter is 0.381 inches with a reduced shank design and a 0.286-inch square drive. It produces 3B class of fit threads.

This tap is suited for production and maintenance threading on carbon steel, hardened steel, and stainless steel workpieces. The extended neck length makes it practical for fixture work, deep counterbores, or any setup where the tap must pass through a bushing or guide before reaching the threaded bore. It is commonly used by machinists and tool-and-die technicians running CNC or manual tapping operations. The steam oxide coating reduces friction and provides moderate lubrication retention during cutting.

Key Features

• Spiral flute geometry ejects chips back out of blind holes for cleaner threading
• 30-degree right-hand helix angle suits a wide range of threading applications
• Modified bottoming chamfer threads closer to the bottom of blind bores
• Vanadium high-speed steel construction handles carbon steel, hardened steel, and stainless steel
• Steam oxide finish reduces friction and improves lubrication retention
• Reduced shank with 6-inch OAL and 1.875-inch neck for extended reach

Compatibility

Designed for threading 3/8-16 UNC right-hand internal threads to a 3B class of fit in carbon steel, hardened steel, and stainless steel workpieces. Part of OSG Series 398.

Installation Notes

Installation and use should be performed by a qualified machinist or toolmaker familiar with tapping speeds, feeds, and cutting fluid requirements for the workpiece material. Secure the tap in an appropriate tap driver or CNC spindle rated for the square drive size before operation. Ensure the work-holding fixture and guide bushings are aligned to avoid tap breakage, particularly given the reduced shank and extended neck geometry. Never force a tap that has stopped cutting — back it out and clear chips before continuing.