The Hornady match grade Bushing is required for use with the Hornady neck sizing die. It is a self-centering, interchangeable Bushing for extreme precision in neck sizing. Notes: - Bushing fits in Hornady match-grade full length and neck sizing die - Bushing is self-centering in die body. Use of Hornady match grade neck and full length dies and bushings: - Hornady match grade dies have a separate, interchangeable neck size Bushing (not included with die). - the dimension of the Bushing (inside diameter, listed) determines the neck size when the brass is inserted into the die. - standard dies size to SAAMI minimum specification and this is often not necessary, as a particular rifle, brass type and chamber may not need minimum dimensions. Less sizing results in less working of the brass. - using some loaded or dummy cartridges that fit the rifle's chamber without excessive play, measure the diameter of the case neck. Subtract .001" from that diameter and the result should be a reasonable starting point for the correct Bushing dimension. Select a size that is at that dimension or just under it. - bushings work in both the neck and full length match grade dies. The bushings are available in .002" increments. - the 242, 244, 246 and 248 bushings are for the 223 Remington and 22-250 Remington cartridges. - the 260, 262, 264 and 266 bushings are for the 6mm PPC and 243 Winchester cartridges. - the 332, 334, 336 and 338 bushings are for the 308 Winchester cartridge. Specifications: - finish: polished steel - diameter: 0.366 inches