Polyethylene Replacement Lid for Oval Cast Iron Boxes Approximate Measurements coming soon. New to our product line is a polyethylene replacement lid for the older style MBX cast iron meter box. Our innovative grid system design allows for a strong part. The lid has UV protection and a snap stainless steel spring lock system that conforms to industry standards. The lid can be molded as a solid lid, with a Neptune recess or an I-tron pocket. We can mold the name and/or logo of your city or county directly into the lid.