Metal headband base. I also have 5mm in the same color, and 3mm and 5mm in silver listed. As shown in the image, there are differences in the opening width. Also, there are some minor scratches here and there, but we will sell them as items that do not have any problems with use, so please understand. Gold has been coated with rust-preventative spray, but we cannot guarantee that it will not change color. Diameter: Approximately 12.5cm (adjustable) Material: Iron Inventory: 3 #SunyaAccessoriesParts