Patent ID: 8448765

Claim:
A coupling comprising: two concentric rings having a common axial direction, the rings being movable relative to each other and defining a clearance between them extending in the common axial direction for receiving at least one ball, the first ring being a coupling member, the second ring being a tubular slipper with a friction surface on an outer surface of the tubular slipper that is away from the clearance and the at least one ball, the at least one ball providing contact between the coupling member and the tubular slipper, at least one of the rings having a first recess with side walls for receiving the least one ball, the friction surface being configured to be displaced in a radial direction when the at least one ball is axially aligned with the first recess and forced to run up the side walls by rotating the rings relative to one another, and the side walls extending in the common axial direction such that the at least one ball continues to run up the side walls and provide contact between the coupling member and the tubular slipper when one of the rings is displaced in the common axial direction with respect to another one of the rings.