A tube plug (10) for a heat exchanger tube (24) employs a housing (12) having a conical bore (21) with a blind threaded cylindrical bore (28). An insert member (14) includes a threaded shank (72) fittable into the blind threaded bore (28) and a conical section (68) with external threads (69). An eccentric assembly (32) at the forward end of the housing (12) helps lock the housing against rotation as the insert member (14) is threaded thereinto. The threads (69) on the conical section (68) contact, and expand, the conical bore (21) until an external surface (22) of the housing (21) is expanded into sealing contact with the internal surface of the tube (24). <IMAGE>
