PURPOSE: To prevent centralization of an injection pressure during molding of a covering part by forming a groove, the volume of which is increased from a surface, positioned facing a gate for injection, toward the opposite surface, in the surface of a coupling pipe during manufacture of a branch hose where three hoses are interconnected through an Y-form jointing pipe.
CONSTITUTION: A jointing pipe 1 formed of glass fiber-reinforced nylon through injection molding comprises a base part 10 with a thick section and branch pipes 11-13 protruded from a base part 10 in three directions. Each of the branch pipes 11-13 is provided on its outer surface with annular protrusion parts 14... for preventing the slip of a hose. A groove 15 gradually spread in a fan-form manner from an intermediate position a point P) between the branch pipes 11 and 12 toward the branch pipe 13 is formed in a base part 10. The jointing pipe 1 through which hoses 21-23 are connected to the branch pipes 11-13, respectively, is arranged in a mold 3 and a molding material is injected through a gate 30 to manufacture a branch hose. In this case, the molding material is caused to flow along the groove 15 and an injection pressure is prevented from centralization to the specified surface of an insert.