Each keychain is approximately 35x38 mm in length and 3mm thick.
Updates (27 April 2016): There were requests from coolarj10 to make it have a detail on both sides, this may correspond to the request. And this video will show the finished result: https://youtu.be/DcaslMAcbS8.
Print with a thick layer of 0.2mm or less to get a good result. Then sanded, caulked and painted.