Redding 73 style steel neck bushings are heat treated and have hand-polished sizing diameters with a surface hardness of Rc 60-62.
The bushings are available in sizes from .185" through .368" in .001" increments, with the specific size indicated by the last three digits of the part number.
This particular bushing has a diameter of .367 inches, falling within the range of the larger available sizes.