Abstract: A cylinder assembly for a plate tumbler lock includes a plate tumbler which snap-fits into an assembled position by pushing the tumbler into its ward until a projecting detent flexes inwardly and passes by a retaining ledge in the side wall of the ward, and thereafter springs back outwardly so that the detent is retained by the ledge. A pair of notches, one located above and one below the tumbler detent, permit the tumbler to flex inwardly as the tumbler detent passes over the retaining ledge to eliminate any significant forces acting between the detent, the side wall of the tumbler ward and the retaining ledge, and thereby minimize the metal deformation of these components.