Pin b in link 3 fits into a hole in end a of link 1. Cylindrical guides d of link 4 fit in holes in prongs c of link 3. Barrel-shaped head e of link 4 fits into spherical half-collars f of link 2. With respect to each other, links 1 and 2 accomplish four turning motions about three perpendicular axes x-x, y-y and z-z and about axis x' -x' , and one translational motion along axis x-x.
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