exemplary embodiment according to fig1 it has two joints in the exemplary embodiment according to the fig2 through 4 it has one single joint accordingly the exemplary embodiment according to fig1 has two joints 26 28 that are located at either end of a central portion 30 whereas the shackle of the second exemplary embodiment only has one single joint 26 the shackle 24 has two side portions 29 31 in the side portions bores 32 are provided for each receiving a respective one of the side members 20 and 22 so as to allow said rings to move freely these two bores 32 at the remote end meaning at the free end regions of the shackle 24 define a plane that coincides with the plane of the sheet in the representation according to the fig1 and 2 in the illustration according to fig3 this plane is normal to the plane of the paper side portions 29 31 each also have a central end in the center of the shackle 24 in the exemplary embodiments illustrated the joints 26 28 are each designed as eyes that interlock with play said eyes being provided at the inner end regions of the side portions 29 31 or on the bit that has two joints at the central portion 30 this specific design of the joints 26 28 provides the thus connected members with a limited three dimensional range of movement the articulation axis is indicated in fig3 by a dot dash line at 34 the specific design of the joint that consists of two.