This Harper’s Ferry made bayonet has a hilt very similar to the Model 1841 Type II bayonet except for the lug slot.  The smooth ribbed brass hilt is 122 mm long and has 16 ribs.  The muzzle ring is flush to the hilt flat and the inside diameter is 22.5 mm.  There is a forward swept heavy cylindrical finial on top of the muzzle ring and a forward swept round finial on the bottom of the guard.  The press stud spring length is 40 mm in length and the press stud flat is notched in the same manner as the Ames style press stud.  There is a small steel rivet through the hilt and tang close behind the guard.    

 The lug slot is chamfered on both sides leaving the stop end squared with no guide slot.  The hilt flat frequently has inspector proofs stamped close behind the muzzle ring and sometimes inside the lug slot.    

A rare few examples have a steel stop inserted at the head of the stud slot.  The steel cross pin is inserted laterally through the hilt at the head end of the stud slot and it can only be seen from the left side of the grip. 

  The curved blade is 552 mm long and has unstopped fullers.  Some blades are stamped US on the ricasso while others are not.  

Rollin Davis, US Sword Bayonets 1847-1865, claims that 7,317 rifles and 9,721 sword bayonets were produced at Harper’s Ferry between 1857 and 1860.  The 21.75 inch (552 mm) curved blades are stamped U.S. on the reverse near the cross guard and bear no other markings.  The overall length is 26.5 inches (673 mm), with a blade width of 1.125 inches (28.6) at the hilt.

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George Moller, American Military Shoulder Arms, claims 7,317 rifles were produced by Harper’s Ferry with a sword bayonet stud that measures .5 inches (12.7 mm) by .3125 inches (7.9 mm).

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John Willyard, U.S. Model 1855 Series of Small Arms, claims that 9,111 rifles were made at Harper’s Ferry and that the number of bayonets produced closely matched the number of rifles.  The dimensions of the bayonet are listed as; overall length of 26.47 inches (672 mm), hilt length of 4.78 inches (121 mm), blade length of 21.69 inches (551 mm), blade width of 1.10 inches (27.9 mm), blade thickness of .80 inches (20.3 mm) and bore diameter at muzzle of .88 inches (22.4).  Slightly less than half of the bayonets are marked US on the ricasso.  Willyard believes that the US on the sword bayonet indicates that the bayonet was inspected and found acceptable for use on arms issued to Federal troops.  Those bayonets without the US were issued to State Militias.  Sub inspection marks such as JB, L, P, SP or 1 can be found on the hilt flat behind the muzzle ring.  Sometimes inspection marks are found in the lug slot or on the top flat of the press stud.  Willyard claims that possibly 14 rifles produced from August 1856 to February 1857 were made with an alignment key before the deletion of the key was ordered in May 1857. 

In May 1860, Harper’s Ferry was ordered to insert a steel stop at the head of the stud mortise in the sword bayonet handle.  A steel cross pin was inserted laterally through the hilt at the head end of the stud mortise.  This pin can only be seen from the left side of the grip.  Due to the lateness of this alteration, bayonets with this steel pin are rarely encountered.