Half Plug Set: The plugs are used to fill the 1/4" hole in the Nantucket basket base. The base is predrilled to fit the mold screw. Once the basket is removed from the mold, the base hole will be plugged by either a cherry or Mammoth plug. The Mammoth plug is also referred to as fossilized ivory or bone plug. It is easier to tap 1 plug into the top hole and the 2nd plug into the bottom of the hole.