To provide a structure where nut is easily fixed or cannot come off and which does not rotate together with a screw in a seat or backrest for a chair where a nut is fitted and mounted to an inner shell from its surface side.
A nut 21 has a threaded cylinder 25 and a hangover part 26. In an inner shell 11, a nut-storing recessed part 22 with which the nut 21 can be engaged in a prescribed attitude and which is long and narrow in a planar view, and a pair of bag shaped parts 32 linked to the nut 21 are formed. When the nut 21 engaged with the nut storing recessed part 22 is rotated leftward, the nut 21 is held so that it cannot come off or rotate so as to allow a part of the hangover part 62 engaged with an inside of the bag shaped parts 32 and a screw 20 to be screw-threaded. A projection 23 for holding the nut 21 so that it cannot return or rotate when unscrewing the screw 20 is formed on an inner peripheral surface 29 of the nut-storing recessed part 22.
Tadashi Higashino
Hiroyuki Nishi
Ryuichi Watanabe