FIELD: medicine. SUBSTANCE: prior to performing the operation, protruding working part of cutting instrument 10 is adjusted by moving and fixing cone 2 of external body 1 with the aid of polyhedral circular lock 11. Cutting instrument is preliminarily secured in collet 19 by means of bushing 22 and clamping nut 23. Operating movement is transmitted from tap wrench by fixed hold-down nut 15 of handle 16 through central rod 6 to drive shaft 7 which has projection 12 and bushing 20. Moving and fixing mechanism 8 along cutting instrument 10 is shifted along axis and coupled to circular projection 12 as a result of overcoming the resistance of spring 9. As soon as hole is drilled, axial load is removed from moving and fixing mechanism 8 which is separated from projection 12 and shifted along axis under the action of elasticity of spring 9. Drive shaft 7 and moving and fixing mechanism 8 are prevented from contacting by spring 9. EFFECT: higher reliability and safety. 1 dwg
