Heli-Coil® STI (Screw Thread Insert) taps are used for general and machine operations. The standard STI tap can be used as a basic tool to create threads ideal for threaded inserts. It is recommended that these taps are used with a CNC machine or other high-precision equipment in order to ensure a proper class of fit.

When preparing a hole to accept a Heli-Coil® wire screw thread insert, a Screw Thread Insert or STI tap is used to prepare the hole. The recommended drill is utilized to open the hole to the correct minor diameter. The STI tap is then used to create the proper threads in the piece. While an STI tap does differ from a standard thread cutting tap, all accepted machining practices should be adhered to. Taps should be fixtured properly relative to the workpiece, and an appropriate lubricant should always be used. Heli-Coil® STI taps are available in several styles to tap into both blind and through holes in various material compositions. As with all Heli-Coil® taps, the class of fit of the final Heli-Coil® assembly is determined by the class of fit of the tapped hole. Therefore, Heli-Coil® STI taps are available in both 2B and 3B configurations. Heli-Coil® can also work with you to develop taps for specialized materials. Our Heli-Coil® Applications Engineering staff can provide you with all of the pertinent details regarding this subject. 


Accuracy of the finished thread when the insert is installed is dependent upon the accuracy of the tapped hole. If the finished tapped hole gages satisfactorily, the installed insert will be within the thread tolerance.

Heli-Coil® offers STI taps in four styles:

  • Standard Plug (4-Thread Chamfer): Easy starting for through-holes and blind holes
  • Standard Bottoming (2-Thread Chamfer): Ideal for blind holes drilled to a minimum depth
  • Spiral Pointed Plug (4-Thread Chamfer): Free-cutting for use in long through-holes and in blind holes with chip clearance
  • Spiral Flute Bottoming (2-Thread Chamfer): Pulls chips out of deep or blind holes in soft materials (not available for metric sizes)

Contact us to receive more information on our Heli-Coil® STI Taps and Gages.

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The availability of the products described on this site, and the product descriptions, may vary from country to country. Consult your STANLEY® Engineered Fastening Account Executive or your local distributor for specific product information.