A hollow plastic product with a substantially tubular section, two open ends and a thread at the outside of one end of the product is removed from a core mold part by closing the threaded end of the molded product and injecting compressed air into the molded product to loosen the molded product from the core mold part. The threaded end of the product is closed by attaching a threaded closure having a matching thread onto the threaded end of the molded product. A robotic arm is used to robotically attach the threaded closure onto the threaded end of the product. The threaded closure is a plastic cap that injection molded in the injection molding system in which the product is injection molded, with the caps being injection molded at the same average rate as the products are injection molded.