Marked with Z6 at the base of the socket and R over a B with a 62 beside it at the front of the socket. Museum collection number painted on the bottom where the whalebone would have been inserted into the adapter. Metal has a nice japanned brown finish.
This scarce bayonet socket was an altered Model 1858 Civil War Period bayonet and was designed to fit the .69 caliber musket. Originally this bayonet would have had a whalebone blade with an India rubber ball attached at the tip. See The American Bayonet 1776-1964, by Albert, N. Hardin, Jr. pp 188-189.