Anet A2 doesn't seem to be getting much love from designers, so I created a fan duct for it. It's for 50x50x15 "turbo" style layer cooling fan. My fan is the cheapest one I found on Aliexpress, the wires were too short, had to extend them. If you have a choice, save yourself the headache and buy a fan with long enough wires (90cm?).
In latest version I have beefed up the mount plates, and enlarged the lower holes to hotend fan to make inserting the screws easier. Use the original hotend fan screws for mounting, with this thicker version you can't keep the original grille (need 2mm longer screws, if you want to keep it). You will need two M3x20 (or slightly longer) screws and 2 nuts to fix the layer fan, and obviously the 5015 layer fan itself.
Added a version with 18mm autolevel sensor mount. NOT TESTED, use at your own risk :)