A coupling assembly for rotatably coupling two shafts comprises a first shaft extending longitudinally between a first end and a second end and having a radially extending flange at said second end; a second shaft extending longitudinally between a first end and a second end and having a radially extending hollow receiving member at said first end, the flange being positioned within the hollow receiving member, The hollow receiving member comprises an inner cylindrical surface comprising at least one longitudinally extending member groove and the flange comprises an outer cylindrical surface comprising at least one longitudinally extending flange groove, The coupling assembly also includes a barrel-shaped roller bearing provided to extend longitudinally within and in contact with both said flange groove and said receiving member groove and the flange groove and/or said member groove has a longitudinal concave barrel shape for receiving and contacting said barrel shaped roller bearing.