Arbors are designed to be used in conjunction with the NRA Laser Boresight. The arbor acts as a sleeve for your boresight and is designed to fit into the chamber of your rifle. Arbor Size Chart .223 bore sights are compatible with the following arbors: AR243 220 Jay Bird, 243 Win, 256 Win, 260 Rem, 7mm-08, 307 Win, 7.62x54, 308, 358 Win AR3006 25-06, 270 Win, 280 Rem, 30-06, 338-06, 35 Whelen AR264 264 Win Mag, 7mm Rem Mag, 300 Win Mag, 300 Weatherby Mag, 338 Win Mag, 358 Norma Mag. AR12 12 Gauge AR7.62x39 7.62 x 39mm, .220 Swift, .303 British AR30-30 .30-30, .32 Win, .375Win, .225Win AR22-250 .22-250 Designed and packaged in the USA.