Abstract: A shaft drive element is disclosed. The device exhibits the characteristics of maximum engagement contact area, uniform pressure throughout the contact area, variability in lockup and release characteristics as determined by the designer, minimum stress concentration in both the drive and driven element, economy of manufacture, self-centering and ease of assembly. The drive member has a cross section defined by six segments of a logarithmic spiral, three clockwise and three counterclockwise joined end to end. The female drive member having a cross section defined by six segments of the same spiral of slightly greater radius.