Abstract: A method of manufacturing a moulded part using a first and second mould, wherein the first mould has a complementary design of the outer surface of the moulded part and the second mould has a complementary design of the inner surface of the moulded part and a boss cavity for forming an outer wall of a thin-walled boss to be moulded onto the inner face of the moulded part. The steps include seating a plug substantially co-planar with the complementary inner surface design and extending the plug into the boss cavity presenting an inner wall of the boss, wherein the thickness between the inner and outer wall of the boss is less than 60% of the thickness of the moulded part where the boss is moulded thereto. Closing the first and second mould forming a mould cavity. Injecting molten material into the mould cavity. Waiting a predetermined amount of time to allow the molten material to harden. Opening the first and second moulds. Extending the plug from the boss cavity.