A plug assembly including a plug, a sidebar movably mounted on the plug, and a plurality rack pins seated in the plug. The sidebar is biased to an outer position in which the sidebar extends beyond an outer surface, of the plug. Each rack pin is a single-piece unitary structure including a key-following leg and a sidebar-engaging leg. The sidebar engaging leg includes at least one true, gate and a plurality of false gates. When a true gate of each rack pin is aligned with the sidebar, the sidebar is free to move radially inward to an inner position.

A rekeyable master lock includes a plurality of pin gears, with each pin gear engaged with a corresponding key follower. As each key follower rides up and down on the key bitting, it causes a corresponding pin gear to rotate. Each pin gear engages a user gear and a master gear so that, as the pin gear rotates, the user and master gears rotate. Each user and master gear, in turn, drives a corresponding user rack and a master rack. When a valid user key is inserted and rotated, the user racks or master racks are aligned along a common axis and held in alignment by a locking bar. Longitudinal movement of the user gear or master gear allows the rekeying function by decoupling and recoupling the user gear or master gear with the user racks or master racks.

In an exemplary embodiment, a plug assembly includes a plug body, a sidebar, a cover plate, and a plurality of rack pins positioned in the plug assembly. A first portion of the sidebar is positioned in the plug and a second portion protrudes beyond the outer surface of the plug body. The rack pins are configured to selectably resist and permit radially inward motion of the sidebar. The cover plate is operable to selectably retain the rack pins within the plug body.