Pin a of link 1 fits into the hole at end b of link 3. Spherical half-collars c, at the other end of link 3, fits over ball-shaped head d of link 4. Round trunnions e of link 4 fit into holes in prongs f of fork 5 . Pin h of fork 5 fits into a hole in end k of link 2. With respect to each other, links 1 and 2 accomplish five turning motions about three perpendicular axes x-x, y-y and z-z, and about two parallel axes x' -x' and x" -x" .