ZN-9R "Round" key's cover is square rather than round. This makes for a stronger cover. The finger pieces extend sufficiently to operate the key with the cover in place. Tony also makes finger pieces that are 1/4" longer.
We use Optically Clear, molded Acrylic. 1/4" plastic is used for most models. A box-end, "dove tail" joint is used to join the pieces. There is NO glue used as it will foul the contacts and attack the finish on the keys.
Any engraving (ie. callsign) is done on the inside so it will not collect dust.
I have made several covers for the ZN-9R. If you have one please provide a photo of the key with its dust cover and we will put it on here.