I had too many failed prints of bgill's "Micro SD Card Holder" http://www.thingiverse.com/thing:1289250 that i planar cut the model in mesh mixer to just 4 slots for a quick print so i can scale the model to correctly fit micro sd cards.
at 110% of original i am still getting stuck cards
at 115% of original i am finally getting smooth action on the cards in an out
PLA 208C 0.2mm layer, 0.4mm nozzle, printrbot simple metal
makes a nice little desk holder to boot
rotate so the slots are on top.
keep scaling the model until sd cards fit.
Outter slots might have an easier fit due to flex of the thin walls and less shells on one side. so ensure you focus on the inner two slots for calibration.
changing filament might change your flow rate and your final fit.
NOTE: this model has NOT been scaled. it is the same as bgill's original.