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Although the overall engine had a serial number of J-2111, the thrust chamber itself has a unit number of 2113.

Picture 2 of 3.

The stencils in this photo are located approximately 180° around from the engine's thrust chamber stencil.

Apparently, it was not uncommon for Rocketdyne thrust chambers to have a different serial number than the completed engine; in this widely-used F-1 manufacturing photo, the thrust chamber on the right side of the photo has a serial number of "2010" while the nearly-completed engine on the left is engine F-2010.