Lamp Finials - the fancy item on the top of a lamp
The item on the left is a finial. The next item (left to right is one which has been prepared by removing the top ball and drilling a through hole.
The next item is a lamp shade riser, and the last item is one prepared by removing the threaded end.
All are available from a well-stocked hardware store. ACE hardware in the States caries them. Most Home Depots & Lowes only carry the risers.