Steel Intermediate (Plug) Lead Taps Cut Threads To a Precise Dimension; The Heli-Coil (R) STI Tap is Oversized From a Standard Tap To Allow For The Wire Insert Once Installed. STI (Screw Thread Insert) Taps are Special Taps That Produce a Larger Than Nominal Hole To Accommodate Heli-Coil Wire Inserts. High Speed