Abstract: A tumbler assembly for a key operable locking mechanism (hereinafter referred to as a "key mechanism"), includes support means (12) and a plurality of tumblers (14) mounted in the support means. The assembly, suitably orientated relative to a three-axis co-ordinate system for which it is appropriate to designate the axes as being vertical, lateral and horizontal, has tumblers (14) mounted in the support means (12) in a random or sequential series which extends longitudinally in the support means. The tumblers (14) are mounted for movement to and away from a respective active position by substantially linear movement. The support means has first (14a) and second (14b) laterally opposite sides, with each tumbler accessible at each of those sides. Each of the tumblers (14) is configured at the first side (14a) for effecting its movement by engagement with a configured key blade of a suitable key presented longitudinally (20) along the first side (14a).