MK8 extruder filament guide

Threading the filament into the bowden tube of the sintron MK8 extruder (http://www.aliexpress.com/store/product/Sintron-1-75mm-3D-printer-Kossel-Mini-MK8-Extruder-for-E3D-Bowden-Delta-Rostock-Free/114769_32429475134.html) is quite troublesome. It often gets stuck at the screw that attaches the bowden tube to the extruder.
This little part fixes this.