Creating contact between teeth with convex-concave geometry and small difference in curves. It was found that the absolute multiplicity of tooth engagement (100%) in compliance with the three defining conditions can occur only when using the variable convex / concave profile of the tooth flanks, usually the central wheels, depending on the values of conical axoid angles and notation the radius of curvature of the profiles of the teeth of the crowns of the satellite wheel, as well as the number of teeth of the Z wheels and their ratio.