Metal Lamp Base retailer decorative Vintage Salvage

We have a Metal Lamp Base decorative Vintage Salvage item. It is a black metal with rust showing through all over, probably a bit more rust than black finish. It measures about 5 1/2" across the center bottom retailer x about 1 1/2" in h with the center hole opening being about 4" across the opening (the very center circle opening is 3/8"). With some tlc this could be a very nice base. I believe it is cast iron.