Typically this plate would be attached to the breech end of a barrel housing and would house the spirit level. The spirit level was used in sighting the gun. The bronze plate measures 3 5/8 inches in diameter and the entire edge is engraved. There is an oval hole in the center of the plate where the spirit level would rest, with 1 hole above and 1 below. On either side of the oval hole are engraved flourishes and in block letters is "GATLING GUN/PATENTED". At 3 o'clock and 9 o'clock are 2 larger screw holes on the outside edge.