(57) Abstract The 1st and 2nd opening end (12,14) it has, at the same time in order these the 1st and 2nd end (12,14) in center, for this formation item to have flexibiility, the bellows section (16) almost the 1st and 2nd end (12,14) the skirt section which it adjoins on the one hand (82) it possesses the tubular it has blow molding item. The bellows section (16) it is formed by blow molding, the skirt section (82) it is formed by compression formation. Form of the execution where this formation item is desirable strengthens the rib which extends to the inner split of the wall of the blow molding department (40) having, the skirt section which is the bellows section and the compressed formation department (82) with the transition region between (42). The parison (80) the die (50) the step which is shut in inside and, next, the core (74) the parison inside the die (80) there is with a step which is introduced inside. The core (74) the thermoplastic material perhaps it makes radial and lap to also direction move to axis direction. Formation of the product to which this manufacturing method, the convex section (126), the rib (40,128,136) or while possessing other inner split projections, had the surface and substantially possesses cylindrical external surface is made possible.
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