An adjustable mechanism for a motor vehicle is used to adjust an adjustable element in a motor vehicle, especially a seating part. Said mechanism comprises a spindle nut comprising an axis, said 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.