Rod b of link 3 fits into bushing a of link 1. Link 3 has spherical surface c fitting into spherical collar d of link 2. Link 3 has round lug e which slides along circular groove f 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 y-y.
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