Tube Plug consists of a tapered spindle & sleeve, which expands when tightened to ensure a close metal-to-metal fit with the tube wall. Each tube plug is packaged with full instructions. Tube plug for a heat exchanger tube employs a housing, which include a conical bore with a blind threaded cylindrical bore. The tube plug comprises a one piece mechanical plug with one open end and one closed end, which is capable of being inserted in a heat exchange tube and internally expanded into contact with the inside surface of the heat exchange tube for preventing flow of a coolant through the heat exchange tube. The tube plug comprises a groove extending around the outside circumference, which has an elastomeric material disposed in the groove for enhancing the seal between the tube plug and the tube.