Countersink seat ribs?

Maybe I'm having a brain fart...On drawing 22 over on the left for the center section there is a note to machine countersink all F904 to seat rib rivets. These would be the tabs on the seat ribs on the forward end where they meet the F904 bulkhead. What do I countersink? The only thing that makes any sense to me is to do the lower surface of the flange on the F904 and not dimple the tabs on the ribs. Anybody have any pictures or advice on this?

Thanks

papamike said:

The only thing that makes any sense to me is to do the lower surface of the flange on the F904 and not dimple the tabs on the ribs.
Thanks

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Yes as you said