Lyman 57 and 66 peep sights have long been favored by shooters and hunters. The 57 is for rounded receivers, such as bolt actions. The 66 is for flat receivers, such as lever action rifles, like the Winchester 94, Marlin 336 or modern shotguns. Features include 1/4 minute audible click micrometer adjustments for elevation and windage, quick release slide, coin slotted (stay-set) knobs and two interchangeable aperture discs (large hunting aperture and small target aperture) for any shooting condition.