An adjustment system is configured to adjust the length of a first strap. The adjustment system comprises a ring defining a first through hole in a first direction. A pin is fitted movable with respect to the ring. The pin partially obstructs the ring in the first direction so as to divide the first through hole into a second through hole and a third through hole separated from the second through hole by the pin. The adjustment system comprises a tab at least partially blanking off the first through hole in the first direction. The tab is arranged at a distance from the pin to define a space for the first strap to pass between the pin and the tab.