the flexspline having a major axis thereacross with a maximum engagement between the gear teeth of the flexspline and the circular spline; the gear teeth on the flexspline having a precessing inclination and back again as they pass from the minor axis to the major axis thereon with respect to the oval shaped wave generator; and the gear teeth on the flexspline and the circular spline having a tooth profile which Acco modates such tooth inclination so as to avoid interference therebetween as they mate.