Abstract: The lock configuration described in the parent application enables a dual key lock to operate efficiently, accurately and conveniently with a single stack of tumblers. Also, the individual tumblers of the invention are typically receivable in the lock in a plurality of alternative orientations in which their gates assume different functions, facilitating key changes. The present application discloses means for further improving the precision of gate positioning in such locks, and remarkably simple and economical means for adapting such locks for either right- or left-hand installation.

Abstract: The invention provides an improved lock configuration by which a dual key lock can operate efficiently and conveniently with a single stack of tumblers. That configuration permits more accurate positioning of the tumblers upon key operation, whereby a larger number of key combinations can generally be accommodated. Also, the individual tumblers of the invention are typically receivable in the lock in a plurality of alternative orientations in which their gates assume different functions. That difference of function may constitute a change of effective gate position with respect to the same key, or may shift cooperation with the two keys from one pair of gates to another. That aspect of the invention is useful in facilitating key changes, especially in locks designed for safe deposit and similar service.