Easy to install and operate, these aircraft grade aluminum and stainless steel sights replace those found in the carry handle and on the gas block of all M4, AR-15, SR25 and AR10 flat top weapons. Both the front and rear sights work in conjunction with all standard height front sights and back up iron sights. These battle sights are built strong for long lasting use. The sights lock into the upright position and may be folded down out of the way by pushing a side-mounted button. Feature hard coat anodizing. Notes: Troy Industries makes two sights; standard and micro. The measurement to the center of the standard aperture is 1.36". The measurement to the center of the micro aperture is 1.16". The standard sights are meant for Mil-spec top rails and the Micros are meant for the enhanced weapons such as the IAR, Robinson Armament XCR, Heckler & Koch 416 & 417, and other weapons with raised top rails. This is the standard height rear sight.