Button comprising a nut (1), a support (3) and a cover (5) fitted on the aforesaid support (3) defining a chamber (6) and having at least one window (51, 52) for an indicator for at least one position chosen from a first position for the button roughly corresponding to a minimum tightening torque for the nut (1) and a second position for the button corresponding to a lower tightening torque than the tightening torque for the first position, with the aforesaid indicator (30) being connected to a plate (13) by a tube element (131) which ensures that a rotation of the plate (13) is translated into a rotation of the indicator (30).