BTW: Dewglass, I still don't see any emails from you (I checked my spam folder also)... did you spell my email address correctly...?
The letter Z in the filename extension .CTZ indicates that the file is Zipped (see the newsletter that Cindy points to above)...
Zipped is a form of compression...
For a given compression method, the size of a compressed file varies depending on the file content.
If the compression method is good and suitable for the file content, then the .CTZ file will be smaller than the .TUN file.
My $0.02.