We manufacture these small billet aluminum fill cap & bung assemblies in house using only domestic material and we make them in a couple of different finishes with either a steel or aluminum weld in bung. The weld in bungs have an 1-1/4" opening, an overall bung diameter of 1-5/8" and feature a step on the backside to make ease of locating while welding. The billet aluminum fill cap is 2" overall diameter.