Inclination of the flexspline tooth will cause mechanical interference with the adjacent circular spline tooth. The interference can be corrected by removing material from the tooth profile, in the tangential direction, of the amount of the arc segment "h(θ)u(θ)”. Half of this amount is removed as by etching, machining or the like from the respective teeth 30 and 32 ofthe flexspline 26 profile and the other half from the circular spline 28 tooth profile. Thus the new equations for tooth profile are