Ghost-ring aperture is a fast, alternative, open sight that will save your hunt if your scope fails. Perfect for use on in-line muzzleloaders when hunting no-scope areas. Attaches in just seconds, without gunsmithing, to any Weaver-style base. Fully adjustable for windage and elevation. Includes front Test Post. Mfg: Xs Sight Systems SPECS: Steel, blue, matte finish. .191" (4.8mm) diameter aperture. Includes 2 Apertures: Large .230 and Small .191 High Weaver: .500" (12.7mm) from the top of base to center of aperture.