Study of the effective depth of the gear tooth root for aeronautical applications. Some of the gear’s thermal treatments which are carried out in AvioAero (Rivalta di Torino) are checked out through the use of flat test samples, suitable to exemplify the tooth flank of a toothed profile. This allows you to be sure of the effective depth reached on the side of the tooth, while often there is no information about another critical area of the gear itself: the gear tooth root, more difficult to reach for the carburizing atmosphere and therefore with an effective depth thinner than what you get on the flank of the corresponding tooth.