Not sure what I am missing, but what screw are you using to attach the Nepton 280L cooling head to the board, nothing seems to fit.
I had to go to home depot and get 8x 3/4" 6-32(think thats what they are, well normal coarse thread PC) screws
The holes for the cooling head at threaded with M3-0.5, which is what Intel uses for their heatsinks.