I.D. Tolerance of +.0001/.0005 Concentricity of 0 to .0003 Total indicator reading maximum Heat treated to Rockwell C62 to 64. No Counterbored All American Drill Bushing are made in the USA from steel obtained from a domestic steel foundry. Our standard bushings are made of C1144 and heat treated to Rockwell C62-64. Concentricity is held at 0 to .0003 T.I.R maximum for ID sizes of 1/8 to ½ and 0 to .0005 T.I.R Max for any other size. A blended Radius on the drill entrance improves drill entry and alignment which prevents tool wear and breakage. All of our products are free of conflict materials of any kind and conform to Reach.