Patent ID: 7617569

Claim:
An articulation, comprising: a first shell having an inner wall provided with a plurality of first teeth; a second shell rotatable relative to the first shell and having an inner wall provided with a plurality of second teeth; a gear wheel movably mounted between the first shell and the second shell and intermeshing with the first teeth of the first shell and the second teeth of the second shell to lock the second shell onto the first shell; a push button movably mounted on the second shell and rested on the gear wheel to push and move the gear wheel to detach from the second teeth of the second shell so as to unlock the second shell from the first shell so that the second shell is rotatable relative to the first shell; and an elastic member biased between the first shell and the gear wheel to push the gear wheel toward the second shell and the push button; wherein the second shell has an inner portion formed with at least one limit slot, and the gear wheel has a first side directed toward the second shell and formed with at least one limit plate, the at least one limit plate extending into the respective limit slot of the second shell when the second shell is locked onto the first shell, and the at least one limit plate separated from the respective limit slot when the second shell is unlocked from the first shell.