Abstract: A flat key has a blade formed with a pair of opposite edges, with a pair of opposite faces between the edges, and with an outer-end tip. The blade further is formed with a pair of relatively shallow, outwardly open, and generally parallel but spaced grooves formed in at least one of the faces and each extending generally longitudinally in a nonstraight path through a plurality of control points from the tip. Each of these shallow grooves has a greater transverse width outward toward the tip from one of its control points than inward from the one control point. A relatively deep and laterally open groove is formed in the one face mainly between the shallow grooves and extends generally longitudinally in a nonstraight path from the tip generally nonparallel to the shallow grooves.