The yataghan blade is 558 mm long and has unstopped fullers.  

From the book SHARPS FIREARMS The Percussion Era 1848-1865, the US Navy order 150 Sharps Model 1855 Rifles with 28 ¼ inch barrels fitted with a bayonet stud & guide on March 14, 1856.  On September 9, 1856 the Navy ordered another 100 rifles with bayonet for a total of 250.  Example serial numbers include 20234, 20404, 20430, 20444, 20446 and 24344. 

The saber bayonets were made by Ames Manufacturing Company and they are believed to be the same construction as in the Model 1853.  The overall length is 27 inches (686 mm). The blade is 22 inches (559 mm) long, 1 ¼ inches (31.8 mm) wide and the fullers are unstopped.  Most of the blades are dated 1856 but some were not dated.  The brass hilt has a 1 inch (25.4 mm) guide slot and a 21 mm muzzle ring diameter.  (It is believed that the muzzle ring diameter listed here is incorrect.) The flat of the hilt was stamped with the serial number of the matching carbine or rifle. 

The early Ames bayonets have a steel post in the brass hilt at the end of the guide slot, apparently to protect the brass from the steel guide bar.  It is not certain when Ames started this practice or when it was terminated but 1855 and 1856 dated bayonets appear to have this feature.

It is believed that the Sharps Model 1853 and Model 1855 bayonets are identical in construction.  A few that are dated 1855 on the ricasso can be labeled as a M1853 because they were actually produced before production of the Model 1855 began.  Also, some examples with serial #s in the 15000 to 19000 range can also be labeled as a M1853 for the same reason. Production of the two models overlapped from 1856 to 1859 and serial #s can no longer be used to differentiate the model without matching the bayonet serial # to the rifle. 

It appears that the frequently quoted statement that all Sharps bayonets have 21 mm muzzle ring diameters is incorrect.  While this may be true for the Model 1859 and M1863 bayonets, all Model 1853 and Model 1855 rifles and bayonets examined so far have been in the 22 to 22.4 mm range.  So far, only those bayonets with the steel post have been dated and only those without a steel post are maker marked. Only a few examples have been seen and a M1855 rifle has not been examined, so the research continues.