Here’s the same filler cap kit we use on all our Camburg 3.50″ rear end housings. The cap is CNC machined from 6061 aluminum, then anodized black. It uses an o-ring seal to the steel threaded bung. The caps OD is knurled to make loosening and tightening easier. The cap is 1.75″” in diameter and has 1-1/4″-12 threads. The weld-on bung is 1.50″ in diameter x ???” tall and has a step on the bottom to fit into a hole that’s ???” to help center it.