This circle is made of brass and has fore and back sights. The fore sight consists of a tall hinged open arch with sighting thread (missing) and a short celestial reflector. The back sight is fixed and consists of a curved bracket containing a small prism. There is a peephole and slit. There are fixtures which may have held filters but are missing. The ring is 0.8" (2.3cm) deep and is flanged on the outside.