I JUST PICKED THIS UP FROM A COLLECTION IVE BEEN PURCHASING OVER THE PAST FEW WEEKS AT AROUND 30 INSULATORS AT A TIME.THIS ONE CAME WITH THE LAST BATCH. I THOUGHT THE RIDGE OF GLASS UNDER THE BASE OF THE UMBRELLA AS ODD. THE 4 OR 5 THAT I HAVE DON'T HAVE THIS RIDGE OF GLASS. ANY THOUGHTS OR IDEAS ????