Abstract: A lock has improved protection against lock picking. The lock comprises plural tumblers, each generally cylindrical in form with outer and inner circumferential edges, all the tumbles arranged on a common axis. The outer circumferential edge of each tumbler having a single true gate, including a void extending a predetermined distance toward the axis and plural false gates, each having a void of lesser extent. Ridges separates the true gate from adjacent false gates, and separate adjacent false gated from each other. The lock also includes a sheath contacting the inner circumferential edges of the tumblers. The sheath includes ridges located to maintain the tumblers in contact with each other.