Link 1 ends in a ball-shaped head with centre 0 which enters conical recess d of link 2. Link 1 is held against link 2 by cover b. Hole A serves to insert the head inside cover b. With respect to each other, links 1 and 2 accomplish two turning motions about axes z-z and y-y which pass through point 0, the centre of the spherical surface of link 1 .
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