1. According to the invention, the fastening part consists of a sintered silver chloride material or includes such a material, the absorbent insert being exchangeably screwed, pushed, snapped, pressed and/or clamped into the fastening part.

2. The drill tool (4) fixed exchangeably by means of a chuck (8) is for this purpose arranged, together with a compressed air drive (9), on a carriage (11) that can be advanced by means of a threaded spindle (10).