I am building a new router table. I am going to make the insert plate myself out of a piece of 1/4 aluminum, mostly because I happen to have the aluminum already. I will need to make inserts, though. What do you think is the best material to use? I have a lot of aluminum and can use that. I could also use a plastic like hdpe. But my question is this:

All the router tables I have used have a notch, screw, or other apparatus to prevent the insert from rotating in the plate. Is this important? My ability to machine the aluminum is pretty rudimentary and I'm not sure I can do much more than make a disc that goes i to a hole.