It was an instrument that allowed the opening up of screw threads in holes. It consisted of a strong base with a longitudinal hole which had pins circumferentially (instead of a female screw) for the driving of the worm screw. At the end of the worm screw there was, transversely, a triangular cutting point (adjustable wedge). The base was fitted onto the perforated processed piece with the worm screw of the base aligned with the hole of the piece. The screw, with the use of hand levers, was turned and consecutively driven within the hole of the piece opening up internal screw threads with its cutting edge.