Abstract: The nut is for repairing leaking bolt holes in flanged pipe joints by means of a closed-end nut having a sharp circular projection on its open end. When this sealing nut is substituted for existing nuts on bolts in the flanged joint and tightened, the nut, which is hardened, cuts a circular groove in the face of the flange that makes a metal-to-metal seal to close leaks at bolt holes. The bolts may be same diameter as the existing bolts and may be installed one at a time to accomplish the repair without reducing pressure in the pipe. Leakage from between the flanges at their perimeter is closed off by sealing in a conventional manner by welding a band around the perimeter of the flanges before the bolt hole sealing is started.