The invention proposes a mechanical assembly for the transmission of axial forces between two secured parts, at least one of these parts having a portion with outer threading, said assembly further including a nut with inner threading able to cooperate with said outer threading to axially block by tightening the other part relative to the first part and to allow the transmission of axial forces between these two parts. The pitch of the outer threading and/or of the nut vary/varies along the axial dimension of the threading, the space gradually decreasing from the first thread to the rear thread in the expected direction for the axial force. The variable threading can be produced by chemical etching.