Helicoil tap drill charts are available online at the Noble Aerospace Private Limited website, the Thor International Pte Ltd website and BarnHillBolt.com. Helicoils are used to fix stripped threads, so that the bolt has something on which to hold securely.
The helicoil itself tends to be stronger than the material into which it is being drilled, which lowers the chances that another stripped thread occurs. A helicoil kit is comprised of a thread tapper, helicoils and drilling tools. It is essential that the tap drill is the correct size to replace the stripped thread, and consulting a chart may help one find the right piece.