Sealing plug

A sealing plug assembly comprising a plug member [and] having a radially outermost cylindrical surface, said surface defining at least one circumferentially extending groove for receipt of an O ring seal therein, a housing [the] for said plug member, said housing defining a bore for location of said plug [and housing including] member therein, co-operating means on said plug member and said housing whereby [the] said plug member may be secured [together the radially outermost cylindrical surface of the plug including at least one circumferentially extending groove within which an O ring seal may be disposed, the housing including an aperture within which the plug is adapted to be located] within said housing, said housing further including at least one radially extending pin moveable between a first position projecting into said base of said housing and a second position in which it does not so project, said pin being adapted to locate within [the] said at least one circumferentially extending groove when [the] said O ring is omitted from the assembly [such as] thereby to prevent [the] said plug member being secured within [the] said housing by [the] said co-operating means.