fastening insert 28 can be seen in detail in the upper part of fig3 as can be inferred from the figure the fastening insert 28 includes a fastening element 29 similar to the fastening element 12 the functionality of the fastening element 29 is essentially the same as that of fastening element 12 but unlike fastening element 12 fastening element 29 has a tapered insertable collar 30 similar to the tapered insertable collar 16 a tie rod 31 and a fastening body 32 in this example of embodiment the tie rod 31 is movably connected with the fastening body 32 in particular the tie rod 31 is connected with the fastening body 32 by means of a swivel connection as can further be inferred from the figure the fastening unit 11 includes a bushing 34 similar to the bushing 17 the bushing 34 is different from the bushing 17 in that an adjustment of the tie rod 31 is possible for the purpose of fastening in particular the connection 33 and the combination of the tapered insertable collar 30 and the bushing 34 facilitates a swiveling motion of the tie rod 31 about an oriented axis in the ambit of the connection 33 transverse to the.