Device for fastening a first component (42) with a through opening (44) on a second component (40) with a through opening (18) being essentially rectangular in cross section, comprising a first fastening element (10) which comprises a radial flange (12) on one end and a shaft section (16) with rectangular cross section, which is insertable into the through opening of the second component and comprising a second fastening element which relative to the first fastening element is at least partly axially moveable, which second fastening element comprises an axial bore for receiving a fastening screw. The first fastening element comprises at least one first section (18) of a first, harder material and at least one second section (20) of a second, softer material, wherein the second fastening element upon screwing the fastening screw is pressed against the second section of the first fastening element and thereby deforming it in a sealing manner.