This was one of the first add-ons I designed and printed for my Anet A8 3D printer. Foremost I saw how the filament was shaving on the extruder. With this part the filament now goes straight through the center of extruder filament hole. I decide just to make a small hole to achieve the least friction on the filament.
The part also holds the cable of the heat element and both fans. In my case it also holds the cable of the proximity sensor.
I've also included a slot in the center support to hold the cable of the extruder cooling fan.
Update 31.12.2016: I've removed the cable holder portion for those that don't need it and added it to the files for download.
Please let me know if you have a problem with the design so I can improve it if necessary.
Also please post a picture with comments if you have made one.
The part was printed at 40mm/s with a 0.8mm shell thickness and 0.8mm top / bottom thick closures.
The "Supports" is recommended for the slot in the support for the cooling fan cable.