The Northern Competition service rifle match sight is one of the finest rear sights we have seen for the AR-15. This is a true one fourth by one fourth rear sight built from solid bar stock. One click value is a true one fourth inch movement at 100 yards. The design and quality of this sight gives the shooter a dependable rear sight with no fitting problems or add-ons to go bad. The Northern Competition rear sight includes an aperture (0.040 inch) and a standard .275 inch hood. The sight is well engraved for easy reference to movements. Tolerances are held tight with threads and screw shoulders precisely cut to reduce play.
Sinclair, Issue:4A, Page:215