That tool is made with a flathead screwdriver bit for stock, a standard dremel type rotary tool with a reinforced cut off wheel, a small flat needle file, and a lot of trial and error. The gap between the prongs is just about exactly the same width as cut of disc. It wasn't easy to make, but I did manage to get it right on my first try, so I guess its not too tough.
Couple of tips: Clamp the bit down to a work surface with something metal. I melted a plastic clamp making that one. Keep a cup of water near by too, to help cool it off for handling and test fitting.
Biggest tip: Buy one of these
and save yourself the hassle. I lost my little bit for a time at one point, and picked one of those up. It worked better than my little tool I made.
For the record, I believe that is rust on the shank.
And yes Squeeker, that's a modded Corsair memory cooler. This
is where I got mine. Here
are good places to find fans for them. (I used the UV orange (non LED) Ace ones, under volted with my fan controller).