3 and ends in a central bore of the tool head 4 in the region of the bits 11 communicates with a ventilation opening 16 formed in the tool head 4 an annular sealing element 18 is provided in an axial sealing region 17 between the tool stem 3 and the tool head 4 the sealing element 18 is arranged in the axial sealing region 17 with a possibility of a limited axial displacement in the embodiment shown in fig3 the tool head 4 the length and cross section of which are selected taking into consideration cushioning properties is formed as a sleeve shaped member the rear coupling section of which has an inner hexagonal cavity in which the hexagonal prismatic coupling region 12 of the tool stem 3 is received a substantially flat end surface 10 which cooperates with a corresponding end surface 10 of the tool stem 3 is defined by an inner annular region having a very large effective radius of curvature the sealing element 18 is arranged about a central sealing region 17 of the tool stem 3 which has a relatively small radial dimension and which engages in the central bore section of the tool head 4 connected with two ventilation openings 16.