Bayonet is in nice condition. The surfaces amazingly nice has gutter on upper surface of blade. US stamp on the bayonet throat. The US Model 1816/22/27 series of bayonets with a nominal 18” blade, face flute of varying length, T-shaped mortise, and a friction fit socket with no locking ring .830” bore diameter for the Model 1816/22/27 bayonet. You would be a nice bayonet for your early M1816 musket.