Fully-coated optics, built-in, fiber optic illumination and 25X magnification provide a close-up view of rifling, crown, breech, chamber, lock work or any critical firearm component. Even inspect empty cases for signs of separation. Variable intensity, LED light emitter is powered by two AA batteries (included) provides a true color image of the surface under inspection. Adjusts to focus from 1mm to infinity. Optic tube fits .17 caliber bores when used without mirror attachment. Mfg: Gradient Lens SPECS: Illuminator - aluminum body, black, anodized finish. Includes batteries and spare bulb. Eyecup - aluminum, black, anodized finish. Optic Tube - stainless steel, .165" (4.2mm) diameter, 7" (17cm) length. Fits 17 cal. and larger. Includes instructions.