A toolholder 12 is provided with a dust cap 14 which is mounted for rotation relative to the main body 15 of the toolholder 12 by means of a bearing 21. The bearing 21 is formed by two discs 24, 27, namely a reinforcement disc 24 and a retaining disc 27, which are separated from one another by a locking ring 26 which is axially fixed relative to the toolholder 12. The reinforcement ring 24 and the retaining ring 27 are held by friction in the dust cap 14 and have clearance permitting movement relative to the toolholder 12. The bearing 21 prevents the dust cap 14 from suffering abrasion or producing an impression on the wall in the event of contact with the latter during drilling. <IMAGE>
