A fitting for insertion of an elongated member, such as a semirigid rod, axially into the end of a live gas main section. The fitting comprises a housing defining a passageway opening which extends axially through the housing. The housing provides, at its opposite ends, exterior and interior openings. The housing is mounted on the main end with the interior opening sealingly engaging and in coaxial registry with the main end. The housing further provides a channel extending generally transaxially of the fitting between the exterior and interior openings. Two closure members are disposed in the channel and are selectively movable therein for increasing and decreasing the size of the passageway opening. The closure members include cooperating gate members and gaskets which define an aperture extending axially of the fitting. The gaskets provide a perimetral seal for the aperture. The aperture has a cross section substantially equal to the cross section of the elongated member. The cooperating gate members and gaskets seal the main end when the elongated member is inserted through the exterior and interior openings and into the main end and the closure members are closed about it. The fitting and semirigid rod are primary apparatus used in inserting a smaller diameter, high pressure plastic gas main into the live gas main. Grease chambers, wire feeds and nipples of various types are used in combination with the fitting to carry out the insertion of the smaller diameter main.