A continuous method of making a dual durometer self-locking, self-sealing plug for filling and sealing holes in panels. The plug is made from two different, chemically compatible thermoplastic materials by coinjection of the two molten components sequentially into a mold and cooling them concurrently...http://www.google.co.uk/patents/US4885121?utm_source=gb-gplus-sharePatent US4885121 - Method of making a dual durometer self-locking and sealing plug
