I have a new CR-10. The fan has 4 indented screw holes (which may be different than other part cooling fans I have seen). The part cooling is terrible and leaves more stringing than it should. I added a lip. You can use the existing screws, and although it's a pain to get the screws in, if you loosen the top 2 also, you can get the stock screws back in (you could always get a slightly longer screw).
I updated this to a better version below with a focussed air flow toward nozzle tip.