PURPOSE: To correct the diametrical dimension of each metallic ring within a small range of tolerance by putting the metallic rings having a segmental part and an inner diameter smaller than the outer diameter of a correcting jig each on the correcting jig and annealing them at a low temperature.

CONSTITUTION: The outer diameter D0 of the correcting jig 2 is formed into a required dimension. The metallic ring (an anti-slip out ring) 1 having a segmen tal part 1a and bent in an inner diameter dimension D1 a little smaller than the outer diameter dimension D0 of the correcting jig 2 each are put on the correcting 2 jig 2. Thereafter, the metallic rings are annealed and treated at a low temperature. The rings are put on the correcting jig having the inner diameter formed into a required dimension and annealed at a low temperature. By this method, the complete roundness of the ring can be elevated.