PURPOSE: To prevent the occurrence of burrs and contrive the reduction of manhours and costs by a method wherein a fourth rectangular projecting part is interposed between a recess part for receiving an inclined push-up core and a third projecting part constituting the opening of a guide groove to form a rectangular notch part at the end of the opening.

CONSTITUTION: A lower die 2 has a top part molding face 20 for molding a top part 12, wall molding faces 21 for molding wall parts 22 for receiving an inclined push-up core 3. The top part molding face 20 is provided with a first projecting part 23 for forming a clip hole 13, a second projecting part 24 having a guide groove 14 formed on its end, a third projecting part 25 for forming an opening 15 on its end and a fourth rectangular projecting part 26 for forming a notch part 16 on its end. This lower die 2 is also provided with the inclined push-up core 3 received in the recess part 22. Since the sliding contact part between the inclined push-up core 3 and the lower die 2 has a sufficiently large area, the sliding contact is easy and accurate. The lower die is locked with an upper die 4 and the molding having a mounting seat 1 is manufactured by injection molding.