Here's the same filler cap kit we use on all our KINETIK race trucks and Camburg 4" rear end housings. The cap is CNC machined from 6061 aluminum, then anodized and laser engraved. It uses an O-ring seal to the steel threaded bung. The caps knurled perimeter make for quick spinning on and off and has a recessed hex head for use of a 1" socket to make loosening and tightening easier. The cap is 3.20" in diameter and has 2-1/4"-10 threads. The weld-on bung is 2.76" in diameter x.600" tall and has a step on the bottom to fit into a hole that's 2.625" to help center it. Here's the same filler cap kit we use on all our KINETIK race trucks and Camburg 4" rear end housings. The cap is CNC machined from 6061 aluminum, then anodized and laser engraved.