Osg 1763901 Spiral Flute Tap 4-40 Unc Modified Bottoming

Product Description

The OSG 1763901 is a spiral flute tap designed for cutting 4-40 UNC internal threads in a modified bottoming configuration. It is manufactured from vanadium high-speed steel and finished with a steam oxide coating to reduce friction and improve chip evacuation. With a 45-degree helix angle and 2 right-hand flutes, this tap pulls chips up and out of the hole, making it well suited for blind-hole applications. It carries a 2B class of fit and an H2 thread limit, delivering controlled tolerances appropriate for standard fastener assemblies. Licensed machinists, tool-and-die makers, and maintenance technicians are the primary installers.

This tap is intended for threading small-diameter holes in stainless steel, high-carbon steel, low-carbon steel, and medium-carbon steel. The modified bottoming chamfer allows threading closer to the bottom of a blind hole than a standard plug tap while still providing modest lead-in. At 2.375 inches overall length with a 0.197-inch thread length, it fits standard tap holders and machine spindles used in manual and CNC tapping operations. It is commonly used in precision machining, MRO maintenance, and light fabrication where 4-40 UNC fasteners are standard.

Key Features

• 45-degree helix angle promotes upward chip flow in blind-hole tapping
• Vanadium high-speed steel construction provides toughness and wear resistance across ferrous materials
• Steam oxide coating reduces friction and helps prevent galling, particularly in stainless steel
• Modified bottoming chamfer enables threading close to the bottom of a blind hole
• H2 thread limit and 2B class of fit ensure consistent, gauged tolerances for standard assemblies
• Right-hand flute direction paired with right-hand thread for conventional tapping setups

Compatibility

Rated for use in stainless steel, high-carbon steel, low-carbon steel, and medium-carbon steel. Fits standard tap holders sized for a 0.194-inch shank diameter. Designed for 4-40 UNC threaded hole applications per OSG Series 303.

Installation Notes

Tapping should be performed by a qualified machinist or maintenance technician using a properly sized tap wrench or machine tap holder. Always ensure the workpiece is securely clamped and the tap is properly aligned before engagement. Use an appropriate cutting fluid for the workpiece material, particularly when tapping stainless steel, to reduce heat and extend tool life. Back the tap out periodically to break chips when tapping blind holes by hand.