RESIN PART, RESIN PART ENGAGING METHOD, AND RESIN PART ENGAGING STRUCTURE

Load required at a time of mounting is made small and engaging force is made large, and both an improvement in workability of a mounting operation and reliable prevention of coming off after mounting are achieved. At an inner side of a U-shaped portion 12 of a weather strip 10, a nipping tubular portion 20 having a hollow portion 24, and nipping lip portions 22 project so as to oppose one another. A communicating hole 28, which communicates the hollow portion 24 with an exterior, is formed in the nipping tubular portion 20. Pressure of an interior of the hollow portion 24 is reduced by a pressure reducing device, and a clearance 30, which is larger than a plate thickness of a body flange 84, is formed. Thus, load required for fitting (load required at the time of mounting) is reduced. When the interior of the hollow portion 24 is restored to atmospheric pressure, a projecting end 20A of the nipping tubular portion 20 is strongly press-fit to the body flange 84. The load required at the time of mounting and an engaging force can be set independently, and an insertion load (the load required at the time of mounting) can be made small and the engaging force can be made large. Thus, an improvement in workability of the mounting operation and prevention of the weather strip 10 from coming off can both be achieved at high levels.