MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
As you can see, I only remixed this thing from an existing one. I moved the ring from vertical to horizontal without doing any measuring. Mine fits tightly on vertical frame and will slip and come off on the top horizontal frame. I don't have my printer at hand now so I can't take the thickness.
None of the 27 "made" before yours complaint about this, so my idea is that your printer is different or your print comes out with different size. However you can simply print it scaling down a bit, like 95\90\85%, and voilà it will fit.