| 摘要 |
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. 13, 1978, entitled "Internal Tumbler Lock Key Change System" to provide an improvement thereof.
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