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If one was willing to peek under the engine, the base of this engine's throat support was visible.

This engine rested on a throat support (a pedestal on which the injector rests which supports the weight of the engine, similar to this J-2 throat support), as an F-1 engine is too heavy for certain models of the nozzle extension to support. This throat support was several inches taller than the interior of the engine, so it was possible to view the interior of the engine if one was willing to peek under the nozzle extension.

The column of F-4023's throat support is visible if one is willing to peep through a nozzle extension pyrotechnic igniter boss.