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View of the outer-dome attach bolt holes and the index holes.

Picture 1 of 2.

There are 64 outer-dome attach bolt holes, to accommodate the bolts which bolt LOX dome and injector to the thrust chamber. There are also two index holes, located 180 degrees apart, to ensure that the LOX dome, injector, and thrust chamber are properly aligned.

Although one of the index pins is round and the other is diamond-shaped, the corresponding holes, seen here between two of the regularly-spaced holes, are of a slightly different diameter. I believe that the diamond-shaped index pin has a larger diameter.

Note that this particular index hole is relatively small, perhaps slightly larger than the outer-dome attach bolt holes (and so I believe it is for the round index pin).

Also note the white, Teflon-filled Flexitallic gasket, used to seal the LOX dome to the injector.