A coupling having at least two concentric rings, each having a circumferential surface and a recess, and at least two roller elements. The roller elements are each disposed in a channel formed by the circumferential surface of one of the rings and the recess of another of the rings. In some example embodiments of the invention, the coupling includes a coupling member with a bearing surface, at least one of the rings includes a split and the split ring is urged against the bearing surface when there is relative rotation between the rings. The coupling member is, for example, a shaft or a gear.