Abstract: A two-piece tube plug for repairing damaged tubes, of condensers, heat exchangers etc., in situ. The plug is made of a thimble having a shell with one end closed and an opposite open end. The thimble has a tapered axial bore in which a tapered cylindrical plug is inserted for expanding the shell of the thimble outwardly radially with the thimble in position on an end of a damaged tube at the tube sheet. The cylindrical plug deforms the shell outwardly radially when driven into the thimble shell to effect a closure on the tube and effect a fluid-tight seal between the thimble and the tube.