This dice is 20mm on each side, each face will need to be sanded to make the edges flush, this is in order to remove all of the burn marks.
First lay out the parts of the dice as shown in the first picture. Then assemble the dice, and apply glue to all of the joints as you assemble it, Use the pictures to help you assemble the dice (same shaped pieces go opposite of each other).
Now you will need to sand the dice so that all faces are flush (the edges stick out so that you can remove the burn marks without sanding away the markings on the dice). Place a sheet of medium(about 120 grit) sandpaper on a flat surface then rub each face of the dice on the sandpaper until it is flat. (Optional) Then using a piece of fine sandpaper lightly sand the faces, edges, and corners of the dice to make it feel more smooth and to remove all sharp edges and corners.
Your dice is now finished and ready for use. I applied a beeswax and mineral oil finish to mine to make it look even better, but this is optional.