Plastic pipe to metal pipe coupling

Claim 1

A PLASTIC PIPE TO METAL PIPE COUPLING WHICH COMPRISES THE COMBINATION OF A SUBSTANTIALLY RIGID PLASTIC PIPE AND A METAL PIPE WITH AN END PORTION OF SAID PLASTIC PIPE AXIALLY DISPOSED WITHIN AN END PORTION OF SAID PLASTIC METAL PIPE, SAID PLASTIC PIPE END PORTION HAVING AN INTERMEDIATE SECTION TERMINATING IN AN END SECTION, A METAL SLEEVE DISPOSED WITHIN SAID PLASTIC PIPE IN CIRCUMFERENTIAL ABUTMENT TO SAID INTERMEDIATE AND END SECTIONS, SAID INTERMEDIATE SECTION PROVIDED WITH GROOVES IN ITS OUTER PERIPHERAL SURFACE WITH THE DEPTH OF SAID GROOVES DECREASING AS A FUNCTION OF THE DISTANCE OF THE GROOVE FROM SAID END SECTION, THE EXISTENCE AND SHAPE OF SAID ANNULAR GROOVES BEING SUBSTANTIALLY INDEPENDENT OF SAID METAL PIPE, SAID METAL PIPE END PORTION HAVING A THICKWALL ZONE TERMINATING IN THE DIRECTION OF THE ORIFICE IN A THIN-WALL ZONE AND THE PLASTIC PIPE THIN-WALL ZONE PROTHICK-WALL ZONE AND THE PLASTIC PIPE INTERMEDIATE SECTION AT THE THIN-WALL ZONE, SAID METAL PIPE THIN-WALL ZONE PROVIDED WITH ANNULAR DEPRESSION IN ITS OUTER PERIPHERAL SURFACE WITH SAID DEPRESSION INDEXED TO ENGAGE SAID GROOVES IN SUBSTANTIALLY INTERLOCKING, COMPLEMENTARY, ABUTTING ALIGNMENT, SAID PLASTIC PIPE END SECTION PROVIDED AT LEAST ONE EXTERNAL ANNULAR GROOVE AND A SEAL GASKET POSITIONED IN SAID GROOVE IN SEALING ENGAGEMENT WITH THE INNER PERIPHERAL SURFACE OF SAID METAL PIPE.