A diameter of approximately 2 1/8 across the top opening area for the burner. It has a small chip on the base that we have tried to show in the photos.Please ask questions or request additional photos if needed. The item "Vtg Green Aladdin Kerosene Lamp Base" is in sale since Tuesday, February 26, 2019. This item is in the category "Collectibles\Lamps, Lighting\Lamps\ Non-Electric\Kerosene". The seller is "eweezygreen" and is located in Canton, Mississippi. This item can be shipped to United States.