The Model 1855 Combination Tool consists of a cone wrench and 3 screwdrivers.  It was adopted in 1855 with the new .58 cal. arms.  It was issued along with the M1855 Band Spring and Tumbler Punch.  Modifications of this tool were issued up through the M1868.  (See Gun Tools, p. 156)

This specimen is marked "US" indicating Harpers Ferry manufacture.