holes 10 of adjacent chamber slots 7 and therefore also the abutment lugs 18 of adjacent plate tumblers 13 are expediently arranged diagonally oppositely as a result of which the chamber slots 7 can be arranged closer together and the cylinder core 6 can be of short design on account of the design of the cylinder core 6 each plate tumbler contains one control step 24 wherein the control steps 24 are arranged laterally at both sides in the key channel 25 yet only at one side with respect to the plane 25 with a spacing to the plane 25 of the frames of the plate tumblers 13 and so as to slide in the same direction during the actuation with a key arrow 40 in fig1 it is possible to design a reversible key 43 having a central continuous middle web or key bit 30 as best shown in fig3 the key bit 30 is rectangular in cross section and has a central longitudinal central axis 41 a height u201c h u201d and a width u201c b u201d two narrow edges 31 32 two wide side surfaces 33 34 and an end edge 35 on one side of a longitudinal plane 42 which extends perpendicular or.