Gear tooth surfaces being in line contact at every instant are considered. The dimensions of the contacting surfaces must be limited in order to avoid: (a) the appearance of the envelope of lines of contact on the generating surface Σ1 , and (b) the appearance of singular points on the generated surface Σ2 . The relations between the developed concepts and Wildhaber’s concept of the limiting pressure angle are investigated. Applications to the worm-gear drive and the generation of a pinion of a Formate gear drive are considered. Computer graphics have been used to illustrate the results of computation.