Osprey Global 223 Green Boresight Kit With All Arbors Black. It is the ultimate accessory for the shooter that needs to sight in multiple guns. The arbors are CNC machined and are meticulously engineered ballistically and schematically. It covers over 20 calibers in one kit. No need to buy separate laser boresights for each gun anymore. Simply unscrew the backing of the arbor or hollow brass piece insert the 223 green laser boresight screw on arbor backing insert into chamber close bolt to power on green boresight and sight in your optics without wasting expensive ammunition