Abstract: A pair of generally coaxial mutually rotatable cylindrical outer ring members (34, 36) are held in spaced apart relationship by three parallelogram shaped relatively thin, flexible, flat planar spring elements (48, 50, 52) which are substantially inextensible in length and are joined to the inside of the outer ring members and held in position by arcuate inner ring segments (38, 40 . . . 46), three for each outer ring member, which respectively span an arc of substantially 120.degree.. The parallelogram shape of the spring elements (48, 50, 52) provides a slanted interconnection between the outer ring members (34, 36). The direction of slant, moreover, determines in which direction the spring elements (48, 50, 52) can flex or bend unidirectionally to relieve the compression stress imparted thereto by any mutual angular rotation of the outer ring members (34, 36).