The U.S. Model 1863 Combination Tool consists of a cone wrench and 2 screwdrivers.  The third screwdriver blade was omitted from the previous M1855 tool due to the fact that the cleanout screw was omitted from the M1863 Musket.    This tool, made in large quantities during the Civil War, was used to manufacture the M1870 Combination Tool and the M1876 Combination Screwdriver. (See Gun Tools, by Shaffer, Rutledge and Dorsey, p. 157)