No doubt there are tons of SD card holders on Thingiverse.  This one has several advantages over others, of various designs.  1.  Single servings.  Why print an eight card holder, when you only need one or two?  Put them anywhere you like, on your Cupcake, Replicator, Ultimaker, or any other printer design with a 6mm or 1/4" material edge.  2.  Open face.  Now you can see which card is in there, without pulling it out.  3.  Easy fit.  I opened things up enough, so as not to accidentally lock the read/write switch.  4. Comes in two flavors.  Metric (6mm), and Imperial (1/4 inch).