Holder for a rotary tool, for example one hole saw

Holder for a rotary tool, whereby the rotary tool is one of a hole saw, a milling cutter, a grinding tool or a reamer, which holder is formed with a rotationally symmetrical holder body comprising a rear drive end, and a front connection end having a connection thread for the connection of the rotary tool using a corresponding connection thread on the rotary tool, that the holder comprises an axially movable thrust collar which is placed at the connection end and around the connection end and which thrust collar has a contact surface facing the connection end of the holder and that the contact surface abuts against the assembled rotary tool, that the holder furthermore comprises an axially movable operating sleeve assembled around the holder body and a number of restraint elements placed in one or more spaces in the holder body and which restraint elements in a first axial position of the operating sleeve are prevented by the operating sleeve from radial movement in said spaces and which restraint elements in a second axial position of the operating sleeve are free to make a radial movement in said spaces, wherein the restraint elements upon said radial movement also are displaced a distance in the axial direction so that a gap between the contact surface and an assembled rotary tool is created in order to reduce the stress obtained between the connection thread and the corresponding connection thread and that each one of said spaces for the restraint elements is limited in the axial direction by a front limiting wall as well as by a rear limiting wall, which two limiting walls constitute parts of the holder body.