and the first v shaped groove 51 is diminished in width the second plate 222 is then swung toward the hanging member 10 two side walls of the second v shaped groove 52 are moved close to each other and the second v shaped groove 52 is diminished also the first plate 221 abuts against the bottom portion of the second plate 222 when the socket 40 is moved toward the hanging member 10 the protrusion 223 is firstly positioned in the groove 42 the first plate 221 and the second plate 222 are moved toward the hanging member 10 the slant surfaces 222 b of the protruding portions abut against and slide along the corresponding slant surfaces 212 b of the ribs of the guiding portion when the second plate 222 continuously slides toward the hanging member 10 and the head portion 224 a touches the fixation portion 211 the slant surface 224 c of the head portion abuts against and slides along the slant surface 211 a of the fixation portion during the slide the region or thickness where the second plate 222 overlapping the guiding portion 212 is getting larger until a top surface of the fixation portion 211 abuts against a bottom surface of the head portion 224 a then the fixation portion 211 engages the restriction groove and the wedging pieces 222 c engage the corresponding hook portions 212 c as shown in fig4 and fig5 since then the total.