an adjustable mechanism for a motor vehicle is used to adjust an adjustable element in a motor vehicle , especially a seating part . the mechanism includes a spindle nut comprising an axis , the spindle nut co - operating with a thread spindle and comprising external toothing on the external surface thereof which is in contact with an additional drive element . the external toothing of the spindle nut is formed by recesses in the external surface of the spindle nut which are inwardly turned in a radial manner , the teeth depths thereof diminishing in the direction of at least one axial end of the spindle nut .