RFID Keyring Profile
cults3d
This thing is an example of reusing and reshaping the popular drop-shaped RFID tag. After some trials and errors, I found the dimensions to draw a perfect profile with a handful of primitives (see the attached figure). I tested such profile with RFID tags from Yarong Tech (link), and another spare tag (don't remember the vendor) and they perfectly fit. However, there are many similar items from different vendors, and they may vary slightly from few hundreds of micrometers. I suggest printing the attached frame to test how your tag fits and eventually apply an offset.
With this file you will be able to print RFID Keyring Profile with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on RFID Keyring Profile.