I have to respectfully disagree. I have heard for years that these were used as Bow Drill Toppers but I have yet to see one that shows the polish inside the hole that would occur from wooden shafts rotating back and forth inside said hole. I never adhered to the "nutting stone" theory either. Why do you need a round stone with hole on both sides to break open a nut? Just put it on a flat surface and hit it with another stone. Viola, a broken open nut. I call them Pitted Stones and I believe most are either Hammerstones or Anvil Stones.
I have a lot of these Pitted Stones and none show polish in the divots.