A key, for use with a rotary cylinder lock of the type having a rectangular key slot and tumbler pins protruding into one or both wide sides of the slot, has a blade with permutations of recesses of different depths (step values) to receive the pins. The recesses are elongated in the direction of blade insertion. At least one of the recesses is located so that its associated pin engages the recess at the end of the recess when the blade is fully inserted so that, after rotation is started, movement of the blade in the longitudinal direction is positively limited.