38 38 a a sealing 42 is inserted between the two sections 20 40 clamp 36 contacts the second section 40 via contacting surfaces 44 44 a sections 20 40 are formed to be planar on the surfaces 46 46 a facing each other and on their outer circumferences they only have the above described contacting surfaces 38 38 a and 44 44 a the manufacture assembly and disassembly of the first section 20 thus require little cost and time as shown in fig2 the clamp 36 can be substituted by bolts 36 a once the packings 32 are worn out they have to be replaced in order for the replacement to be simple safe and quick an assembly comprising first section 20 packings 32 and interface 6 is taken out of drive apparatus 2 after clamp 36 and interface 6 have been released an identical assembly provided with new packings 32 is inserted in drive apparatus 2 clamp 36 and interface 6 are then closed again in a sealing relationship drive apparatus 2 may be put back in operation after only a short standstill the second section 40 is formed to be integral with interface 10 to which gear 16 is attached a further element of interface 10 is flange 48 to which drill stem 12 is bolted bolts 50 are only schematically shown the circumferential surface 52 of interface 10 i e the end of second section 40 facing drill stem 12 is formed as an outer gear rim a gear 54 is in mesh with this outer gear rim 52 wherein gear 54 is caused by drive 14 to rotate in operation drive 14 comprises a motor 56 in the present case this is an electric motor however hydraulic or.