You may have seen these used in my work.
They are called “butterfly or bow tie keys” and have a structural purpose by stabilizing/repairing cracks in wood since centuries.
The opposing wedge shape prevents the crack from getting bigger. They should be 50 to 75 % of the thickness of your wood in order to be effective.
If your table is 2 inches the butterfly key must be at least 1 inch or 1 1/2 inch thick. Any thinner and it’s decoration only.
I make mine out of several materials; Wood, silicon bronze, and brass.
Here are some examples from past table commissions :
