Here's a pic of what mine looks like,its the one in the top row middle of the five.http://www.econobelt.com/e-store/Pulleys.jpg

Look at the bottom row,this is how it will start out in the milling process,now if we put this on a lathe(with shaft to hold before parting) we can then turn the sides and at the same time reducing the teeth pitch to the desired depth and then we end up with something on the top row pullys.

If I had a lathe it would be simpler to show rather than explain.