A gun-drill comprises a cutting-head detachably secured to a shank, having a common longitudinal axis and comprising mating peripheral surfaces. A shank coupling portion comprises a forwardly tapering shank fixation surface is formed at a front end of the shank, and a cutting-head coupling portion comprising a forwardly tapering cutting-head fixation surface is formed at a rear end of the cutting-head. Both the shank and the cutting-head coupling portion extend over a peripheral coupling angle phi of more than 180°. The shank and the cutting-head are assembled by positioning the cutting-head leading face in front of the shank trailing face, slidably inserting the cutting-head coupling portion into the shank coupling portion laterally to the axis of rotation A and rotating the cutting-head relative to the shank in a direction opposed to the direction of rotation R so that the cutting-head coupling portion and the shank coupling portion interlock co-axially.
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