Ruger MK 1, MK II Universal slide mount Not a rib mount Slides onto the receiver Fits all Ruger MK I/II .22 and 22/45 models; all barrel lengths Blue finish Rings not includedRuger MK 1, MK II Universal slide mount Rings not included.Ruger GP 100 Rib Mount 6" non ported Full length base fits 6" barrels Replaces both front and rear sights to attach Weaver dovetail Rings not included