Mechanism for a chair, in particular for an office chair, with a base support which can be placed on a substructure and with a backrest support, wherein the backrest support is pivotably connected to the base support about a first transverse axis, with a spring mechanism for mechanism for adjusting the swivelling resistance of a backrest of the chair, wherein the spring mechanism has at least one spring element, wherein the at least one spring element acting between the backrest support and the base support, wherein the spring mechanism comprises at least one spring end positioning element, wherein the at least one spring element engages with its rear spring end, viewed in the longitudinal direction of the chair, on the spring end positioning element and with its front spring end, viewed in the longitudinal direction of the chair, on the base support, wherein the spring end positioning element is connected to the backrest support via a coupling element in such a way that the spring end positioning element is moved forwards in the longitudinal direction of the chair by pivoting the backrest support about the first transverse axis backwards in the longitudinal direction of the chair, which causes a movement of the rear spring end in the direction of the front spring end and thus a loading of the at least one spring element, wherein the spring end positioning element is pulled forwards in the longitudinal direction of the chair, wherein the spring end positioning element being arranged at a distance from the first transverse axis, characterised in that the spring mechanism has a spacer acting between the first transverse axis on the one hand and the the spring end positioning element on the other hand, which spacer distances the spring end positioning element from the first transverse axis. with a base support which can be placed on a substructure and with a backrest support, wherein the backrest support is pivotably connected to the base support about a first transverse axis, with a spring mechanism for mechanism for adjusting the swivelling resistance of a backrest of the chair, wherein the spring mechanism has at least one spring element, wherein the at least one spring element acting between the backrest support and the base support, wherein the spring mechanism comprises at least one spring end positioning element, wherein the at least one spring element engages with its rear spring end, viewed in the longitudinal direction of the chair, on the spring end positioning element and with its front spring end, viewed in the longitudinal direction of the chair, on the base support, wherein the spring end positioning element is connected to the backrest support via a coupling element in such a way that the spring end positioning element is moved forwards in the longitudinal direction of the chair by pivoting the backrest support about the first transverse axis backwards in the longitudinal direction of the chair, which causes a movement of the rear spring end in the direction of the front spring end and thus a loading of the at least one spring element, wherein the spring end positioning element is pulled forwards in the longitudinal direction of the chair, wherein the spring end positioning element being arranged at a distance from the first transverse axis, characterised in that the spring mechanism has a spacer acting between the first transverse axis on the one hand and the the spring end positioning element on the other hand, which spacer distances the spring end positioning element from the first transverse axis.