Most repairs to furniture during the construction process are a drag because I am kicking myself for making an error in the first place. Not so when adding wooden keys to a slab tabletop.
Big wood tends to split. And left unchecked, the split can continue to open during the seasonal expansion and contraction cycle. The traditional fix is a wooden key that looks like two dovetails kissing. Or a butterfly. Or a unicorn sparring with its sacred mate.
While I am sure someone has written rules and regulations regarding wooden keys, I have yet to read and obey them. I make mine so they have the same slope as my dovetails, and they are thick enough to reinforce the slab.
How thick? I’m patching a split in some 12/4 oak in this example. My key is about 1/2” thick. Depending on how I feel, I might put a key on the underside as well.
(Note there are non-traditional ways to keep a split in check.