the movable upper leaf 1 further has a fastening plate 102 for fastening to a panel 600 the driving ratchet wheel 11 has two ends each has driving ratchet teeth 110 formed thereon to engage with driven ratchet teeth 320 formed on a lateral end of a driven ratchet wheel 32 housed in a lower barrel 21 of the lower leaf 2 the two ends of the driving ratchet wheel 11 further have respectively an indented trough 111 which has two jutting keys 112 formed on an upper side and a lower side opposing to each other the ratchet plane 113 is formed on the peripheral surface of the driving ratchet wheel 11 and has a screw hole 1130 formed in the center thereof to couple with and fasten to the upper barrel plane 1000 of the upper barrel 10 at a selected angle to facilitate assembly the lower leaf 2 has a center notch 20 and two lower barrels 21 formed at two ends each lower barrel 21 has a lower barrel plane 210 formed on an inner top side thereof when the driving ratchet teeth 110 do not engage with the driven ratchet teeth 320 and the movable upper leaf 1 subjects to a weight on the upper side the lower barrel plane 210 contacts a driven ratchet plane 324 formed on the driven ratchet wheel 32 to restrict the.