Spherical surface b of barrel-shaped link 3 fits into spherical half-collars a of link 1 . Link 3 (sliding member) slides along square guide c of link 4 which has two square lugs d at its ends that slide along guide slots e of link 2. With respect to each other, links 1 and 2 accomplish three turning motions about the three perpendicular axes intersecting at point 0, and two translational motions along perpendicular axes in a plane square to the plane of the drawing.
$108$EM,MJ$