We are now going to create a slot through the rings to allow the locking pins to slide through. This is easily accomplished by creating a sketch on a plane offset from the hollow end cap by a couple inches. It should be rectangular, and have a hundredth of an inch tolerance based on the size of the slot that we cut in the rings (the font size). It should be as tall as the retaining rings, so that it should cut completely through the rings. Then, we can cut extrude it to the back face of the end cap.