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Detail of the upper LOX dome inlet on the center F-1 engine.

This engine mockup has the older, twin-elbow LOX dome inlet which was replaced with the more familiar "fish mouth" LOX dome inlet starting with engine F-2003, which means that the only remaining engines with the twin-elbow LOX inlet are these early engine mockups and F-1001 at the National Air & Space Museum (although, unfortunately, I did not know about the differences in the LOX dome inlets at the time of my last visit to NASM, so I have no photos of F-1001's LOX dome inlet).

It is difficult to actually see the the twin-elbow LOX dome inlets on these early engines, as they are either mounted on Saturn Vs (FM-101 and FM-106 on the KSC Saturn V; FM-102, FM-104, and FM-105 on the USSRC Saturn V), and therefore only a short distance from the S-IC's heat shield; mounted horizontally on a wall, simulating being mounted on a Saturn V (F-1001 at NASM); or 19 feet in the air (FM-103 in the KSC Rocket Garden). It took some creative camera positioning to get these photos.

Other than the actual twin-elbow vs. fish mouth shape, these older LOX dome inlets can be identified by the "bulge" shortly inboard of the flange connecting to the LOX valve and by two vertical welds (compare to the single horizontal weld on the later LOX dome inlets).