Abstract: Conventional tumbler type locks are capable of being breached by lock picking tools, punches, drills and the like. This particular lock includes a plurality of flat strip tumblers mounted transversely in a cylinder and which are positioned relative to one another when a flat key is inserted. The key edges are symmetrically shaped and the edges of different keys are shaped differently so that any number of variations of keys is possible. When the correct key is inserted into the lock, slots cut in the upper sides of the flat tumblers align at which time a knife edge strip clears the aligned slots. When the key and lock are turned, the member engages serrations formed on the upper sides of the tumblers thus locking same into position. The upper side of the member engages an interior cam formed on the casing thus moving the member into engagement of the aforesaid.