Metal Plus Spool Holder

I had an idea for a spool holder that sits on top of my Printrbot Metal Plus. The printer design is such that you can just set a spool up there, and it pretty much works, but I was worried it might fall over or something.

I took the 80mm gap at the top, and used pieces from http://www.thingiverse.com/thing:178862 to create a spool holder that rests on top of my printer and fits into the gap, but uses the bearings instead of just resting on the bare metal.

I used a couple 1/4 20 lag bolt