This is a mounting bracket for a 50mmX15mm radial fan to be used on a CR-10 (or CR-10s). In this specific setup, I'm using an E3D beside it, but I believe it'll also work with a stock CR-10 hotend setup. The blower aims directly just below the nozzle. The bracket simply snaps around the metal collar washers connected to the top V-wheels. The cooling fan is only one-sided, but I haven't seen any huge issues since I started testing this about 6 months ago.
The E3D sock is necessary for this setup. Otherwise, the hotend won't maintain a consistent temperature.