A tensioning device comprising a receiver housing, a lever arm mounted on the receiver housing and rotatable with respect to the receiver housing around a first rotation axis, a pulley mounted on the lever arm and rotatable with respect to the lever arm around a second rotation axis parallel to the first rotation axis, and a spring mounted between the receiver housing and the lever arm and adapted to apply a torque for rotating the lever arm around the first rotation axis. The receiver housing and the lever arm are screwed together around the first rotation axis. The spring applies an axial damping effort, parallel to the first axis, on cooperating threaded portions respectively provided on the receiver housing and on the lever arm.