Regarding the thread above about the C-H electric service panel, I'm now convinced that the holddown screws on the main breakers are required and should be there.
So this is for a new panel; what about older existing ones? F'rinstance, my friend with his old Federal Pacific panel (ugh, yes, I know, but it's working fine); his main breakers are backfed. Should they have holddown screws? Do such panels even have threaded holes for such screws?