Abstract: A hammer-drill or the like has a chuck formed with a first bore and with a second bore which intersects the first bore. A tool bit has a shank that is receivable in the first bore and is provided with a surface recess transverse to the elongation of the first bore. A locking stud is received and axially shiftable in the second bore between one position in which it extends through the recess and locks the tool bit in the first bore, and another position in which it is retracted out of the recess. An arresting arrangement is provided which normally arrests the locking stud in its tool-locking position, and which can be operated to release the stud so that the same can be moved out of this position.