Abstract: A slider base has a slider lock combined therewith so as to be selectively and laterally displaced between a locked position and an unlocked position. The mount has a passage formed therein so as to receive a leg portion of the slider lock, the passage including a locking shoulder formed between an upper compartment and a lower compartment so as to face downward. When the slider is set in the locked position, the leg portion of the slider lock is located under the locking shoulder, and when the slider is set in the unlocked position, the leg portion of the slider lock is located so as to be capable of being inserted into the upper compartment by depressing the mount toward a lower position against an urging force of an urging device.