24 the restoring member 54 is formed with a press portion 56 biased between the wall of the receiving chamber 24 and the surface of the pivot arm 11 of the locking member 10 the restoring member 54 has a first end formed with a bent locking end 55 locked in the locking portion 240 of the receiving chamber 24 and a second end formed with a bent locking end 57 locked in the locking portion 111 of the pivot arm 11 of the locking member 10 thereby providing a restoring effect the second end of the connecting member 20 is formed with a shaft hole 21 that has an axial direction vertical to that of the shaft hole 23 and a pivot shaft 40 is extended through the shaft hole 310 of the pivot arm 31 of the mounting member 30 and the shaft hole 21 of the second end of the connecting member 20 so that the second end of the connecting member 20 is pivoted on the pivot arm 31 of the mounting member 30 the shaft hole 21 of the second end of the connecting member 20 has an opening end formed with a receiving chamber 22 having a diameter greater than that of the shaft hole 21 the receiving chamber 22 has a wall formed with a locking portion.