A lock assembly, comprising:
- a lock shell having a front end, a rear end a longitudinal opening accessible from said front end, and an inner surface provided with a set of first tumbler holes disposed adjacent to said front end and a set of second tumbler holes disposed adjacent to said rear end;
- a driving shaft axially disposed in said longitudinal opening and having a transverse head portion, a tail portion journaled on said rear end of the lock shell, and a shaft portion which is rectangular in cross-section;
- first and second plug halves received in said longitudinal opening and cooperatively forming a cylindrical member in sliding contact with said inner surface of said lock shell, each of said first and second plug halves having a clamping face provided with an axial first notch, said first notch of said first and second plug halves cooperatively confining a rectangular receiving space, said shaft portion of said driving shaft extending into said rectangular receiving space and being clamped by said first and second plug halves, each of said first and second plug halves having a curved surface formed with at least one axially extending second notch which opens from a first end of said first and second plug halves and having a terminating end spaced:
- from a second opposite end of said first and second plug halves to provide a groove-free space between said second end of said first and second plug halves and said terminating end of said second notch;
- a biasing means to bias each of said first and second plug halves toward said transverse head portion of said driving shaft;
- a key plug rotatably mounted to said lock shell inside said longitudinal opening adjacent to said front end, said key plug being formed as an annular wall confining an axial key way and having a set of third tumbler holes aligned with said first tumbler holes when said lock assembly is in a locked position, and a
- rear end provided with first and second axially extending arc projections to engage said transverse head portion of said driving shaft;
- a first set of holding means resiliently extending through said first and third tumbler holes into said key way to engage said lock shell and said key plug when said lock assembly is in said locked position;
- a second set of holding means resiliently extending through said second tumbler holes into said longitudinal opening;
- and
- a key having a cylindrical key body provided with radial pits, and a front end formed with first and second axially extending curve protrusions which define a receiving groove therebetween, said first and second curve protrusions having different lengths;
- said key being inserted in said key way such that said first set of tumbler means engage said radial pits so as to engage said key body with said key plug and disengage said lock shell from said key plug thus permitting rotation of said key plug relative to said lock shell, said curve protrusions moving said first and second plug halves away from said transverse head portion against said biasing means to align said groove-free space of said first and second plug halves and form a continuous annular path, said second set of tumbler means contacting said first and second plug halves at said annular path to permit rotation of said key relative to said lock shell;
- whereby, when non-alignment of said groove-free space of said first and second plug halves occurs due to insertion of a wrong key into said key way, rotation of said key plug by the wrong key causing said second set of tumbler means to engage said second notch of said first and second plug halves and prevent further rotation of the wrong key and said key plug relative to said lock shell.