The utility model provides a special stifled bits instrument of numerical control lathe, includes: before prevent bumping ring (1), sealing washer (2), body (3), spring leaf (4), spring (5), the rear defence bumps ring (6). Special stifled bits instrument of numerical control lathe body (3) are cylindrical, both ends are equipped with the external screw thread, outer wall axial symmetry is equipped with two rectangular slots (C), respectively be equipped with an arciform spring leaf of rectangle (4) in the groove (C), the centre of spring leaf (4) respectively is equipped with one spring (5), the right end screw thread connection of body (3) the rear defence and bumps ring (6), before, left side end screw thread connection prevents bumping ring (1), the rear defence bumps ring (6) and before prevents bumping ring (1) and pushes down spring leaf (4) both ends. The utility model is suitable for a numerical control lathe processing processes the screw thread, prevent effectively that waste scrap iron from getting into oil pipe in the course of working in, improve oil pipe and restore the quality, avoid the pressure test machine hank detain or the pumpingh well production process in card pump failure takes place, practice thrift the operating cost, increase crude oil production.