This is a spare engine skirt for the F-1 rocket engine currently on display at the Udvar-Hazy Center (A20050101000). The skirt increased the expansion ratio of the engine and, by consequence, raised the maximum thrust.
NASA Marshall Spaceflight Center transferred the skirt to the Museum in 2004. It was built by the Rocketdyne Division of Rockwell International Corporation.
Transferred from NASA/Marshall Space Flight Center