STI TAPS
An STI tap thread tap is designed to create an oversized thread to accommodate the required Heli-Coil insert. Screw Thread Inserts (STI) are helically formed diamond shaped stainless steel or phosphorous bronze wire that screw into a threaded hole to form a mating internal thread. Screw thread inserts are a convenient way of repairing stripped out threads and are also used to provide stronger threads in softer materials than can be obtained by directly tapping the base metal.
Spiral-point STI (screw-thread insert) taps have straight flutes with a spiral point that pushes chips in front of the tap as it moves into a hole and out the other side, eventually forcing the chips out of the hole. They are used for creating oversize internal threads in through holes so a helical-coil screw-thread insert can be installed in the hole. The insert distributes the load across the length of the threads and improves the threads' strength when a fastener with a standard screw thread size is installed in the hole.