Toothed belts and pulleys are of major importance in synchronous drives based on flexible components. These components enable problems to be overcome efficiently and very economically, problems that would otherwise require the use of kinematic motion gearing or transmissions with articulated link chains. In fact, the performance provided by synchronous belt drives is analogous to the characteristic performance of both chains and gearing however belts and pulleys by comparison have additional advantages deriving from their structural features.