The Jeg's filler cap is not your ordinary style cap that had been run through a screw machine with just a knurled edge. We start with 2-1/2'' 6061 aluminum bar stock, turn the basic shape with 1-1/2''-12 thread in a CNC lathe, then we machine the hand grips and the Jeg's logo in a CNC mill. Next we send it out for a clear anodized finish and add an o-ring seal. The weld fitting is also CNC machined from a generous block of aluminum or steel creating a heavy duty mount. These can be used as a rear end filler and an inspection port, overflow tank cap, valve cover cap, dry sump tank filler cap or whatever your fabricating mind can think of.