Abstract: A tilt adjustment-locking mechanism for a seat back includes a rotating locking mechanism part attached to the seat body and a fixed locking mechanism part that may tilt with the seat back which are connected together by a cam. The fixed locking mechanism part includes an interior-toothed area to which an exterior-toothed area of the rotating locking mechanism part forming a part of a tumbler drive fits. Clamping areas overlapping the fixed and rotating locking mechanism parts are provided. At least one of the locking mechanism parts includes a polygonal circumference area. These areas are engaged against numerous polygonal surfaces on the matching surfaces of the circumference area in the receptor opening on the seat back or the seat body so that it may not rotate, and whose exterior circumference is entirely surrounded by a clamping area.