Link 1 has two ball-shaped heads, a and c. Head a fits into spherical collar b of link 3. Head c fits into cylindrical hole d of link 2 . Link 3 slides between flat surfaces e of link 2. With respect to each other, links 1 and 2 accomplish two turning motions about perpendicular axes x-x and y-y, and one translational motion along axis x-x.
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