Abstract: A lower pair kinematic assembly has two relatively movable mechanical members, such as relatively rotatable columns of a radial drilling machine, which slide relatively to each other through interfitting conjugate surfaces equipped with a hydrostatic bearing system. When pressure is supplied to the hydrostatic bearings the surfaces can slide relatively to permit relative movement of the members, but when the bearings are inoperative the surfaces interfere with each other to lock the members together automatically. The interference between the members may be adjusted hydraulically.