211 is formed coaxially through the inner core 21 and aligns with the through hole 11 of the base 10 each one pin chamber 212 is formed longitudinally in the front end of the inner core 21 each locking pin 214 is mounted slidably in a corresponding pin chamber 212 and selectively protrudes out of the corresponding pin chamber 212 each spring 213 is mounted in a corresponding pin chamber 212 and presses against a corresponding locking pin 214 the securing protrusion 215 is mounted securely in the inner surface of the inner core 21 and may be mounted securely in the mounting hole 31 to secure the inner core 21 to the knob 30 with further reference to fig5 and 6 the lock core 22 is cylindrical is mounted rotatably in the lock core cavity selectively engages the inner core 21 has a front end a rear end a shaft 221 a key groove 222 and may have at least one pin hole 223 and at least one pushing pin 224 the rear end of the lock core 22 abuts the front end of the inner core 21 at a surface interface the shaft 221 is formed on and protrudes coaxially from the rear end of the lock core 22.