PROBLEM TO BE SOLVED: To provide a joint construction of a resin tube, which has resistance to thermal deformation or vibration occurring in a joint body, the tube and a cap nut, can maintain strong tightening of the joint body with the tube, suppress the rotation of the cap nut in the middle even when the cap nut is loosened from a screw, and can connect or disconnect one resin tube to/from the other resin tube or the tube to/from a fluid device.;SOLUTION: In the joint structure 1A, a diameter expanding end 11 of the resin tube 10 is fitted into the joint body 20, and an inside screw part 55 of the cap nut 50 is screwed with an outside screw part 25 of the joint body. The screw shape of the outside screw part of the joint body and the inside screw part of the cap nut screwing with each other is formed in cross section as a polygonal shaped portion 23 forming a polygon having five to thirteen vertices. The longest distance from the center of the outside screw part to the polygon is 1.001 to 1.07 times the shortest distance from the center of the outside screw part to the polygon.;COPYRIGHT: (C)2010,JPO&INPIT
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