Double bitted-reversible key plug lock

A lock having a locked condition and an unlocked condition comprising a barrel having a front end and a distal end and a circular internal bore having a first diameter and a longitudinal axis, the bore having a first, a second and a third longitudinal spline, with the first and second longitudinal splines being radially opposed and terminating before the front end of the barrel, and the third longitudinal spline oriented intermediately to the first and second splines, and extending through the front end of the barrel;

• a substantially cylindrical plug adapted to reside in the bore, the plug having a substantially rectangular bore, the bore having right and left side walls;
• the plug also having a first, a second, and a retaining transverse cylindrical spring pocket, each spring pocket having a diameter and a bottom wall, and a first, a second and a retaining transverse tumbler slot, with each tumbler slot having a depth, the spring pockets and tumbler slots located sequentially along the longitudinal axis with the tumbler slots extending through the bore and the spring pockets alternating between a right side and a left side of the bore, and the diameters of the spring pockets greater than the depth of the tumbler slots;
• first, second and retaining tumblers slidably positioned in each respective tumbler slot, each tumbler having an internal opening having a wall and an arm, each arm extending into a respective spring pocket;
• a spring mounted in each spring pocket between the bottom wall and a respective tumbler arm for biasing the tumbler radially outwardly with the first and retaining tumblers biased in one direction toward the first spline and the second tumbler biased in the opposite direction toward the second spline, with at least one of the first and second tumblers positioned at least partially in the respective spline in the absence of a key to define a locked condition;
• a first reversible key having longitudinal side walls adapted to extend into the plug bore and through the tumbler internal openings, the key having a first and a second land, the lands located to interact with the first and second tumbler internal opening walls when the key is fully inserted into the bore;
• wherein, when the first key is fully inserted into the plug bore, the first and second lands move the first and second tumblers against the bias of the respective springs so they retract from the respective splines and the plug can be rotated from the locked condition to the unlocked condition with at least one of the first and second tumblers aligned with the third spline;
• a second reversible key having longitudinal side walls adapted to extend into the plug bore and through the tumbler internal openings, the second key having a first, a second and a third land, the lands located to interact with the first, second and retaining tumbler internal opening walls when the key is fully inserted into the plug bore,
• wherein when the second key is fully inserted into the plug bore while in the unlocked condition, the first and second lands move the first and second tumblers so the respective tumblers are either positioned in the third longitudinal spline or fully retained in the plug, and the third land moves the retaining tumbler to be positioned in the third longitudinal spline, so the plug cannot be rotated in the barrel but can be retracted from the barrel.