From the known history of the World War I era and the artifact markings, this is likely a right-hand tractor Lang propeller for the single engine U.S. Navy VE-7 Bluebird multi-purpose aircraft built by the Lewis and Vought Corporation.
Lang Propellers was a leading British manufacturer of the World War I period. Dashwood Lang took out a patent in 1909 for “an improved formation of the blades of propellers for use on airships and aircraft where greater efficiency is secured.” The curvature of blades having a “convex side and a flat side” was described in the patent application. Lang was a principal supplier to Sopwith, and was bought out by that well known aircraft builder in early 1917.
But when the United States entered World War I, the Navy needed propellers in high volume and provided funds for Dashwood Lang to found the Lang Propeller Company of America in August 1917.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.