Abstract: The invention contemplates an improved drill-bit construction wherein the shank by which the bit is clamped is characterized by (a) three angularly spaced grooves which are continuous over their entire length of engageability to the jaws of a multi-jaw chuck, (b) at least one of the grooves being closed at its rear end, (c) the rear end of the closed-end groove is at no greater offset than 5-mm from the rear end of the bit, and (d) the diameter of the cutting part of the bit shank is greater than the diameter of the clamping part of the shank, to an extent which at most results from shaped formation of the chip-removal groove.

Abstract: 1. A tool holder for drilling machines, drilling devices as well as drills and drill sets.2. The tool holder, which is developed as a multi-jaw chuck, has a cylindrical bore 326 into which, with maximum opening of the holder, the jaws 322 engage, or the driver of each jaw has an end surface 416 which faces the hollow space of the holder and is interrupted by an axially extending rib 320.The drilling device has a tool holder developed as multi-jaw chuck and a drill whose chucking shank is guided axially in the hollow space of the holder and has grooves for the engagement of radially inner parts of the jaws of the multi-jaw chuck.In its chucking shank the drill has axially extending grooves for the engagement of the jaws of a multi-jaw chuck, within the bottom of which grooves, or at least in one of them, there is a trough which terminates at a distance from the rear end surface and is connected with said end surface by an introduction groove whose cross section is smaller than the cross section of the groove.