lower part of both sides of the inner housing 208 and connect the bases of the claws 209 and the outside the snap rings 212 are snap rings for shafts that include an e ring and a c ring and the snap rings 212 are fit into the grooves formed around the pressing bodies 211 to prevent the pressing bodies 211 from falling the compression springs 213 are loosely fit into the bases of the core beams 215 so as to press the lower part of both sides of the inner housing 208 and the operating part 214 and the compression springs 213 energize the operating parts 214 to the outside in the pressing parts 210 when the operating parts 214 are pressed down the ends of the core beams 215 press the bases of the claws 209 to elastically deform the claws 209 protruding on the sides of the protruding part and the claws 209 are stored in the grooves 220 when the press of the operating parts 214 is removed the pressing bodies 211 are returned to prescribed positions by the compression springs 213 and the claws 209 simultaneously return to a state in which the claws 209 protrude on both sides that is their initial state the engaged part 207 has a concave part 218 which is removably engaged to the protruding part 217 of the inner housing 208 the lower part of the concave part 218 is substantially formed into a concave part where a step 219.