Abstract: Extending between the plug and the housing of a pin tumbler lock are two diagonally opposed rows of columnated locking tumbler pins with or without master pins which establish two individual shear lines between the housing and the plug. An operating key, which is insertable centrally within the plug in a single orientation therewith, is provided with a pair of bitted surfaces which respectively contact the columnated pins in the respective rows. The columns of the master pins and locking tumbler pins in a first of the rows have thicknesses and numbers which may be collectively different from those of the columns of the wafers and locking tumbler pins in a second of the rows to form a unique coupling arrangement along each of the shear lines between the plug and the housing. The above structure including the two rows is combined with the invention described in co-pending patent application, Ser. No. 752,084, filed Dec. 20, 1976, now U.S. Pat. No. 4,094,175, patented Jun.

Abstract: A pin tumbler cylinder lock having a plug rotatable within an external housing, the housing and plug having a row of axially aligned locking bores, a key slot in said plug in alignment with the bores, the lock bores having space for springs, wafers and locking tumbler pins positioned and sized to permit the plug to be operated with a predetermined operating key to lock and unlock the lock when the operating key is inserted into the slot; the housing having a row of auxiliary aligned bores angularly offset from the locking bores, the auxiliary bores having springs and master wafers, the springs biasing the master wafers inwardly toward the plug; and the improvement comprising a relatively thin-walled shutter sleeve fitted for rotation around the plug, the plug being adapted to rotate within the shutter and/or therewith, a row of axially aligned locking bores in said shutter in respective radial and axial alignment with the locking bores in the housing and the plug; first means within the housing and the shutte