A plug system for sealing a tube having two axially positioned plugs, each of which includes a tubular housing having a deformable wall that surrounds a threaded inner bore and an insert member having a threaded post corresponding to the inner bore, a ramped surface positioned to deform the deformable wall outwardly when the threaded post is advanced into the first inner bore, and a first driving recess having a that is positioned oppositely from the first threaded post. The first plug may be installed in place using a driving recess in the rear of the plug to form a first seal in the tube. The second plug may then be interlocked with the driving recess of the first plug and installed in place to form a second seal in the tube.