This is just a basic plug to fill in the hole at the back of the build chamber when the spool mount is not in use - this helps create a fully enclosed build chamber.

There are some other great design available but I created this one for its simplicity and fitment. I also have another plug design available to fill the handles: http://www.thingiverse.com/thing:775815

Printed with ABS to withstand high temperatures and at 0.1mm resolutions to improve tolerance.