Guhring 9039880095250 Cobalt Sti Tap 3/8-16 Unc 3 Flute

Product Description

The GUHRING 9039880095250 is a cobalt spiral flute STI tap designed for cutting Screw Thread Insert (STI) internal threads in demanding metalworking applications. Built from cobalt high-speed steel and finished with a titanium nitride (TiN) coating, this tap delivers extended tool life in abrasive materials. It cuts a 3/8-16 UNC thread profile to a 3B class of fit, with a 40-degree right-hand helix angle that efficiently evacuates chips upward during through-hole and blind-hole tapping. The modified bottoming chamfer allows threading closer to the bottom of a blind bore than a standard plug chamfer. Overall length is 3.381 inches with a 0.367-inch shank diameter.

This tap is suited for machining alloy steel and unalloyed steel in production and job-shop environments. The STI thread form produces an oversized internal thread that accepts helical wire inserts, restoring or reinforcing thread integrity in high-stress assemblies. It is used by machinists, tool-and-die makers, and maintenance technicians working on precision components that require thread insert installation. The 40-degree helix angle promotes smooth chip flow and reduces the risk of chip packing in deeper holes. Series 3988 from GUHRING represents a dedicated STI tooling line appropriate for CNC tapping centers and hand-tapping with proper alignment fixtures.

Key Features

• Cobalt high-speed steel construction for improved heat and wear resistance in steel alloys
• TiN coating extends cutting edge life and reduces friction during tapping
• 40-degree right-hand spiral helix for efficient upward chip evacuation
• Modified bottoming chamfer allows threading nearer to blind-hole floors than plug-chamfer taps
• 3B class of fit provides standard tolerance for general-purpose STI threaded assemblies
• 3 flutes balance chip clearance and core strength for reliable performance in steel

Compatibility

Designed for cutting 3/8-16 UNC STI internal threads in alloy steel and unalloyed steel workpieces. Accepts standard 0.367-inch round shank tap holders and collet-style tapping chucks sized for that shank diameter.

Installation Notes

This tap should be installed by a qualified machinist using a properly aligned tap holder or tapping head to prevent thread lead error and tap breakage. Always apply cutting fluid rated for steel when tapping to reduce heat buildup and extend tool life. Confirm spindle speed and feed rate match manufacturer recommendations for cobalt taps in the workpiece material before beginning the cut. Inspect the tap for chipping or wear before each use and do not force a worn tap to prevent breakage in the bore.