Abstract: A plug assembly for fluid sealing a pipe includes a cylindrical plug made of pliable material which has a conical bore defining a cylindrical wall of tapering thickness. A threaded bore or stud extends axially of the bore and has a nut rotatable mounted thereon. A spherical or conical drive member carried by the bolt contacts and expands the tapered wall of the plug when the nut is tightered on the bolt. The nut may bear against the drive member or one end of the plug. The bolt may be prevented from rotating when the nut is tightened, by shaping one end of the bolt to engage a wrench, or by locking the other end of the bolt in the plug and providing gripping means on the plug arranged to engage the inside of the pipe.