Dome Sealing Plug

The forward face of the F-1's LOX dome had sixteen threaded holes through which inner-dome attach bolts passed to help secure the injector to the LOX dome.

Dome sealing plugs were screwed into the threaded holes to protect these bolts. They worked so well that the bolts were in pristine condition and still had grease on them after decades on the ocean floor.

I was later able to more extensively photograph another dome sealing plug from a different F-1 engine.