Dimension is 20x4.6x12.2mm (inside where the USB reader resides) printed using flexible TPU. Have not try with other material, do it at your own risk.

Purchase this microSD card to USB reader from aliexpress. The key ring pop out from reader after awhile. Found out the inner part can be pull out. This design is for holding it and add it to my key ring.

Edit: I edit my design to add a version that slides in for PLA or ABS, have not test