It cracks me up how so many people answer this question by saying, "Use a Dremel tool." What I'm guessing you would like to know is the method for determining the shape and position of the new openings. I have the same plane and stuffed a ZDZ40 into it! The 18/8 prop was way too big for the included spinner. You might consider using the following method. Buy a profile gage for about seven bucks, push it down over the prop where the spinner would be, and make a template of this shape out of file folder stock. Tape the template over the original opening using the opening's leading edge as a reference and carefully scribe the shape on the spinner. Repeat this step on the other side. (Make sure you have the template facing the right direction!) Cut away at the spinner with whatever cutting tool(s) that you like. Balance the spinner and back plate. I think you'll find that the spinner end up with a more or less square opening, except for a bit of original opening that remains.