The Sightron SIII Long Range Rifle Scope features a 30mm tube for added strength and better light transmission. Each Sightron SIII is nitrogen filled to prevent fogging and is also water, fog and shockproof. The Zero Stop may be the easiest and quickest on the market. The rotating lock ring does not require any knob removal or shims as in other models. To set the zero stop, simply sight in the gun, rotate the zero stop and tighten the lock ring set screw and you are set to go. Other features include easy to adjust target style turrets, side parallax adjustment, and a fast focus eyepiece.