Abstract: A positive axial clutch including a first inner having a surface of revolution about the axis of rotation of the clutch, which surface is substantially a hyperboloid through every point on which two straight line generators may be drawn so as to lie wholly in the surface. A second outer race defined with the first inner race, an annular space between confronting surfaces of the races, one of which is the surface of revolution. A plurality of thrust transmitting rollers are disposed in the annular space between the races so as to engage with the surfaces thereof to make thrust transmitting contact between confronting surfaces for driven rotation of the first or second races in at least one direction, with each roller contacting the surface of revolution of the first inner race along a generator of the surface or a line which approximates to such a generator. The rollers are all similarly inclined with respect to radial planes.