Hertel K007321AS Spiral Flute Sti Tap 1/4-20 Unc Hss

Product Description

The HERTEL K007321AS is a spiral flute STI (Screw Thread Insert) tap designed for cutting internal threads that accept Helicoil-style thread inserts in 1/4-20 UNC applications. Built from high-speed steel with a bright finish, it features three flutes wound at a 52-degree helix angle, which efficiently evacuates chips upward out of the hole during blind or bottoming-hole operations. The bottoming chamfer allows threading close to the bottom of a blind hole, making it suitable for repair work and close-tolerance insert installations. Machinists and maintenance technicians use this tap when restoring stripped threads or installing wire thread inserts in steel, aluminum, and similar materials.

This tap is suited for production and maintenance environments where 1/4-20 UNC Helicoil insert preparation is required. The STI thread form is oversized relative to standard 1/4-20 geometry to compensate for the insert wall thickness, producing a finished thread that accepts standard 1/4-20 fasteners after insert installation. It is appropriate for use in manual tapping operations and light CNC or drill press applications where controlled feed is maintained. The overall length of 2-23/32 inches allows adequate reach in most standard workpiece setups.

Key Features

• STI thread form sized for 1/4-20 UNC Helicoil-style wire thread inserts
• 52-degree helix angle promotes efficient chip evacuation in blind holes
• Bottoming chamfer threads close to the base of blind holes
• High-speed steel construction provides good wear resistance across common workpiece materials
• Bright finish for visual inspection of tool condition
• H2 thread limit for controlled fit tolerance in insert applications

Compatibility

Compatible with Helicoil insert installations referencing Helicoil reference number 5905-4. Designed for use in 1/4-20 UNC STI tapping applications where wire thread inserts are being installed.

Installation Notes

This tap should be installed and operated by a qualified machinist or maintenance technician familiar with thread insert procedures. Always secure the workpiece before tapping and use an appropriate cutting fluid to reduce heat and extend tool life. Apply steady, controlled feed pressure and back off periodically to break chips when tapping deep holes. Inspect the tap for chipping or wear before each use, as a damaged tap can produce out-of-tolerance threads that compromise insert seating.