Barrel-mounted, dovetail Bullseye sight gets you on target fast with perfect alignment for improved accuracy. Steel, double-ring peep design ensures consistent sight alignment and helps improve shooting form. The moment the rear sight is misaligned, the front sight drifts out of the center ring, telling the shooter to re-align. Replaces standard 3/8" dovetail rear sights on many rifles. For use with bead-type or traditional blade front sights. Mfg: Marble Arms SPECS: Steel, blue, polished finish. Fits nominal 3/8" (9.5mm) dovetail. Outside Ring O.D. - 9/16" (1.4cm). Inside Ring I.D. - .15" (3.8mm).