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A throat support next to the thrust chamber.

When a rocket engine is displayed vertically, the thrust chamber may not be strong enough to support its own weight, and so a throat support is inserted underneath the engine. The engine's injector (near the top of the engine assembly) rests on the throat support, which bears the load.

The most obvious use of a throat support I've seen is F-1 engine F-5036 when it was in front of Building 4200, which appears to be levitating. The J-2 formerly in front of Building 4200 also sat on a throat support.