| 摘要 |
A selectively rotatable cylinder for a lock has a cylinder housing with a bore extending along an axis. A cylinder plug having a keyway therein is rotatable in the bore about the axis. The plug is connected to a driving means for actuating any connected lock mechanism. In the cylinder body and cylinder plug are pin tumblers adapted to be positioned by a key in the keyway. An upper tumbler pin in the cylinder body is spring-pressed toward the keyway. A portion of the cylinder plug in the transverse plane of the upper tumbler pin is cut away to provide a substantially chordal cam surface or ramp extending from the periphery of the plug to a radially inward intersection with the keyway. The upper tumbler pin follows the ramp and moves toward the axis as the plug is turned by a key in the keyway. The side of the key encounters the lowered upper tumbler pin after a predetermined amount of rotation about the axis, thus preventing further rotation of the cylinder plug. A special key with a cut-out slot when located in the keyway and turned passes or clears the lowered tumbler pin and affords additional plug rotation about the axis.
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