The filament spool mount on the MakerGear M2 works great -- if you have the thick-edge spools like MakerGear uses. For other spools, the mod suggested by http://www.thingiverse.com/thing:37210 works way better (and both can be mounted simultaneously for easy switching). Unfortunately, MatterHackers and some other filament vendors often use spools that have very small core holes, and the rod suggested by Thing 37210 will not fit through....

This is a simple push-on end cap with an interior designed to firmly grip a standard 3/4" wooden dowel as shown. Without these silly little end caps, the uneven winding of some spools can cause the dowel to walk out of the spool... which would be bad.

Instructions

Start by making most of Thing 37210, then make this end cap instead of the one in Thing 37210.

This end cap is an easy print in ABS or PLA. The "M2" label is at the top while printing, which leaves a span, but any mess will be hidden because the span is inside the end cap. You need 2: one for each end of the dowel. They don't get glued on because you need to take one off to pass the dowel through the center of the spool.

Incidentally, the 3/4" dowel should be about 8" long.