This is made to be mounted on a Printerbot Metal Plus. It can unroll without stress a filament spool (designed for 53 mm hole --> Parametric files are included if you need another diameter (FreeCAD format, thanks to them for their nice software)). The little thingie is there to hold the spool holder tight on the shell of the Metal Plus.
You need to print :
four "thingies",
two main holders (mirror it in between so you get two symmetrical version),
and two bearings.
The thingie is provided on short and long version to accomodate with little deviation of dimensions (I use three long and one short, but it might be different for you. This thingie is not long to print so just try it out).

The bearing are "print-in-place" design. That works well but requires light supports. You may have to liberate the balls prior to using it. The spacer helps them hold in place. Join the two spacer parts using a 4mm bolt