Alternative part cooling fan duct for Geeetech A10. Supplied fan IMHO is weak. Standard 24V 40x40x20 fan with this duct for me is better solution. In blender file there are three separate objects which You can manipulate according to Your needs and finally create single part with boolean->union and then export to STL.
For ABS print You may increase part size by 0.5% (multiply all with 1.005) due to ABS shrinkage.
There is no significant bridging issues at bottom part of duct for ABS filament and there is no need for internal support which could be hard to remove and may cause blockage.
You need to tap holes for fan and mount to original fan place first with longer screws on bottom and shorter on top and then screw fan to duct with M3 25mm bolts and washers.
to adhere on Geeetech "super plate" add Brim at least 25 lines for ABS print. Devildesign ABS or ABS+ hotend temperature 240 and bed 90 deg. Celsius work for me