After some discussion with Walter (wanderson), it turns out that the original design is too narrow for a printrbot spool and 0.75mm too short for a Makerbot spool.
This is a slight re-design which covers both of these issues allowing for spools that have a width of just under 90mm and a measurement from the outside of the spool to the opposite part of the inner hole of 130mm.
The design is still small enough to fit within the build volume of the Printrbot metal and can be printed without support.
Print without supports.
Use the holes to fit onto the rods (this is a tight fit and will hold it nicely in place.
Put your spool in place, feed the filament through the guide and happy printing!