another different tool bit is shown and the shank has two pairs of axially elongated grooves 46 47 axially offset and displaced through 90 u00b0 relative to one another so that both control elements 16 16 39 can engage into the grooves note fig4 in each pair the grooves are located diametrically opposite one another the axially extending grooves 46 47 are located in the region of the shank between the entrainment grooves 48 and the opening into the holder 1 the slide 12 can move axially over the radially inwardly displaced control elements 16 16 39 and contact the pot shaped stop part 49 extending transversely across the forward end of the holder 1 the part 49 is fixed to the holder 1 in the axial position reached when the slide 12 contacts the stop part 49 the switching member 21 couples the gear wheel 25 with the guidance cylinder for providing the highest rpm the arrangement of the axially elongated grooves 42 46 47 in pairs arranged diametrically opposite one another permit the insertion and locking of the shank 41 45 in the alternative rotationally spaced locking positions afforded by the probe device to change tool bits the slide is displaced in the insertion direction of the tool bit shanks 7 41 45 into the tool by manual operation of the actuation sleeve 13 as described previously displacement of the slide releases the control elements 16 16 39 for radially outward movement and the control elements reach a switching position as shown in fig1 to 4 after a tool bit has been inserted into the holder 1 and the slide has been released for return toward the forward end of the tool in the hand held tool depicted in fig5 to.