This is from the Code Disk detail page:
Imperial Code Disk:
A stepped cone shape appearing to be 3 disks stacked on top of one another.
Occasionally a 2 stepped version is seen, such as on the Snowtrooper Commander.
The bottom disk is 1" (25.3 mm) the middle disk is 3/4" (19.1 mm) and the top disk is 1/2" (12.7 mm.)
There is an indentation in the center of the top disk about 1/4" (6.4 mm)
These code disks are most often found on officer hats and imperial belt buckles.
Occasionally they are found on various helmets

- 400px-Imperial_Code_Disk.jpg (13.33 KiB) Viewed 25283 times
I think the middle one looks the best, but would recommend a metallic aluminum/silver/chrome colored paint.
These look decent, and It's always fun to make stuff but just fyi there are highly polished, machined aluminum discs available from several sources for about $5.