Bottle cap inc. Bottle caps have been manufactured specifically for use in craft and jewelry products. There is no writing or insignia on any of our bottle caps. We leave off the rubber liner typically found inside of all bottle caps. Our bottle caps are manufactured from tin plated steel, then painted and sealed with a food grade lacquer coating. Bottle cap inc. Bottle caps meet the new, 2012 cpsc standards for lead and cadmium content. Our standard sized bottle caps are 1-inch interior diameter.