Thanks. Yes, exactly: 1/4" steel dowels that fit into corresponding aluminum inserts in the sides (the keep the holes from ovalizing over time).
PreDesign- I have some some crazy detailed and fine extrusions. I remember one that was about a 1/4" diameter tube, and the inside had maybe 10 tiny little radial fins .010-.020" thick to transfer heat from whatever fluid passed through the tube. It was some sort of spacecraft cooling component. That detail has to be proportional to the surrounding wall thickness though (just like an injection molded part) to prevent distortion problems as the part cools.