Insert ring for spline coupling

A spline coupling comprising:

• a male spline having a plurality of spline teeth separated by keyways;
• an insert ring comprising a plurality of U-shaped segments each having a pair of side walls separated by a gap and interconnected only by a proximal end wall, each U-shaped segment configured to be received in one of the keyways of the male spline with the side walls being against surfaces of the keyway and the gap leaving a portion of the keyway exposed, each U-shaped segment connected to adjacent U-shaped segments only by a distal end wall to leave a portion of the spline teeth exposed between each pair of adjacent U-shaped segments, a distal opening being defined between the distal end walls of adjacent pairs of the U-shaped segments, and sized to allow spline teeth of a female spline to pass therethrough;
• and
• the female spline having a shape complementary to that of a combination of the male spline and insert ring for coupling engagement therebetween, with the spline teeth of the female spline passing through the distal openings during the coupling engagement.