Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:1697121.

Simple spool holder designed to go on the stock arm to allow you to run smaller .25kg and .5kg spools that do not fit over the stock holder.

I've also included a foot so you can use it stand-alone for other printers as needed. If the foot fits loose, just shim it with a little piece of paper/tape. Or Glue it in if you're not using it with the Mini's stock arm.