Plastic cap
thingiverse
Just needed a plastic cap for a hole in some aluminum. Its was a quick and dirty make, but worked well. Scale it up and down to match your hole size. Also scale it in the Z direction if your aluminum plate is thicker.
Download Model from thingiverse
With this file you will be able to print Plastic cap with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on Plastic cap.