Holder for a rotary tool which holder is formed with a holder body comprising a rear drive end and a front connection end having a connection thread for the connection of the tool. The holder comprises a thrust collar having a flat contact surface facing a connection end of the holder. The holder comprises an axially movable operating means, a number of restraint elements placed in one or more spaces in the holder body which restraint elements in a first axial position of the operating means are prevented from radial movement in said spaces and which restraint elements in a second axial position of the operating means allow radial movement in said spaces. Each one of said spaces for the restraint elements is limited in the axial direction by a front limiting wall and a rear limiting wall, which two limiting walls are parts of the holder body.