This is a socket bayonet manufactured - or modified - from the period of 1855 to about 1872; it was the predecessor to the US Model 1873 "Trapdoor" Springfield 45-70 series bayonets. The Model 1855 saw action in the Civil War and probably more of these were used than all other bayonets of the period combined. They are typically American in design in that they do not have a blade "shoulder" and have deep fullers, whereas British bayonets of the period had a shoulder and had shallow fullers that stopped at the shoulder of the blade.
These are attached by fitting them over the barrel muzzle, and fastened into position by means of a mortise slot and locking ring.
All metal construction.
These were designed to fit the various US manufactured .58 muskets, and the 50-70 Springfield "Trapdoor" Rifles prior to 1873.
Blade length is about 18" and muzzle ring diameter is ~0.781" (internal); socket length is ~3".
Scabbards were leather sheet-metal drag, tear-drop finial; leather belt loop, riveted.

I have been asked many questions about how to determine the difference between the US Model 1873 "Trapdoor" Springfield 45-70 and the US Model 1855; I will try to shed some light on this:

• These two bayonet models are virtually identical in every respect with the exception of the muzzle-ring internal diameter. The diameter on the M1855 (and M1855/1870) is ~25/32", whereas the M1873 is 47/64".
• To complicate matters further, many M1855s were "cold-shrunk" to actually fit the M1873 "Trapdoor" Springfield Rifles.
• On November 18, 1863 the M1855 underwent a slight modification to the mortise slot on the muzzle-locking-ring - an additional 2/10" was cut into the slot to allow a more positive lock. This became known as the "Type 2", whereas the original unaltered versions became the "Type 1." This can be identified when comparing the M1855 Type 1 to the M1855 or the M1873; the muzzle locking ring - with screw/clamp assembly placed in a vertical position, but on the same plane as the blade shank - on the M1855 (Type 1) the mortise slot will be virtually touching the slot stop-pin, whereas the M1855 (Type 2) will have the mortise slot up off the slot stop-pin by about 2/10" (if you allow the locking to rest on the pin you will see that the screw/clamp portion of the locking ring is offset to the right of the blade shank and no longer on the same vertical plane.
• Virtually all M1855 bayonets are finished "in the white" or "bright finish"; virtually all M1873 bayonets are gun "blued" finish. There are exceptions, but this is a good general rule.

Please Note: These are currently being reproduced and offered by various distributors. Beware of these being offered as originals by secondary sources.