This specification describes a new anchor or rock nut which is used in association with an anchor bolt to rupture packages of two or more component setting mixtures. The nut is characterized by having a plug of thermosetting resinous material formed in situ which plug may be removed by the anchor bolt...http://www.google.es/patents/US4556350?utm_source=gb-gplus-sharePatente US4556350 - Mine roof anchor bolt
