Abstract: A bearing for rotatably mounting a rotational part, for example a turbine rotor of a dental handpiece, has a plurality of roll bodies, in particular balls, arranged between an inner bearing ring and an outer bearing ring, a cage surrounding the roll bodies in an axial direction, and a locking element for axially locking the bearing rings with respect to each other, wherein the locking element has a ring-like or ring-segment-like securing element fitted on an inner circumference of the outer bearing ring or on an outer circumference of the inner bearing ring in a region of the cage such that the locking element blocks the roll bodies in the axial direction.