The Troy Industries folding front Battle Sights feature push-button operation and tool-less adjustment. Constructed of aircraft aluminum with stainless hardware. Battle Sights feature a zero cant mounting system ensuring perfect sight alignment. Sight mounts to the receiver with a cross bolt. Handguard height are for mounting on a rail system, will not work with shorter railed gas blocks. Gas Block height are for use with railed gas blocks. Notes:This is the Standard HeightThe 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.