Plug, to seal connection openings in water pipes when under test, has a structured outer thread at the far end extending from a flange with a ring seal

The plug (1), to seal water pipe connection openings while the system is tested, has an outer thread (2) with a length (L) at least equal to the outer diameter (D1). The thread section extends from a flange (3), with a recess (4) on the side towards the thread to take a ring seal (7) projecting (A) from the flange surface. The free end (5) of the plug, away from the flange, is shaped to be used by a tool. A further outer thread (6) is between the flange and the free end.