Redding's Titanium Nitride Neck Bushings are heat treated steel with a Titanium Nitride coating to increase surface hardness and reduce friction.
The bushings come in sizes ranging from .185" through .368" in .001" increments, with the specific size indicated by the last three digits of the part number.
The product in question has a diameter of .314 inches, suitable for precision resizing of cartridge necks.