Abstract: A method of repairing a diametral surface of a mold of the type used in manufacturing glass containers by an I.S. machine, after a repair procedure that causes or can cause an out-of-roundness condition in the diametral surface. The method, which is applicable to the frusto-conical baffle match surface of a parison mold and to a compound cylindrical and frusto-conical bottom plate engaging surface of a blow mold, involves positioning a mold set with its separable semi-circular molds in end to end contact and contacting the diametral surface to be repaired, while the mold set is stationary, with a rotating reaming tool the tips of the removable blades of which define a surface that is complemental to the surface to be repaired.