Just thought since I had all the trouble wth the cage sizes I would let everyone know I contacted Martins about the problem with the r640 and this is their response

Hello Kim,
Thank you very much for your suggestion. We truly appreciate it. We catch ourselves "assuming" sometimes because we work around pets and cages all day, every day so it's so much appreciated when we receive suggestions like yours.
The R-640 is a travel/transport cage. Once in a while I'll use the R-640 to separate boys and girls from a small litter but of course they're not in there very long. <g> Never crossed my mind to have it listed as such like our travel cages on our ferret page. We'll get that on our website designer's to do list. Thanks so much!
Diana Martin