I detect the beaches of the OBX often. That piece could be from one of the 100+ shipwrecks in the Graveyard of the Atlantic. Or from a damaged pier, dune sign, modern fishing boat, boardwalk drain cover, etc. But I’ll go with slave ship port hole cover, late 1600’s....
The bar across the back appears to have a "thumb Bolt / Dog" type device, it may have been a locking bar so the grate would stay closed, and on one side it appears that there may have been two hinges.
Fantail water step circa 1922, used only in US waters due to patent restrictions enforced by Swiss Navy. It was in all the papers. Actually I have no clue but I’m sure it dragged your finds pouch off.