The Prodigy Disc naming system is designed to help players figure out what disc they need for each shot quickly and easily. The letter in the model name represents the type of disc. For example, the 'M' in M4 stands for Midrange Disc. The number in the model name represents the stability of the flight path. Our models range from 1 to 7 - '1' being the most overstable and '7' being the most understable. Therefore, the "4" in M4 means that it falls in the middle of our stability rating, making it a slightly understable, depending on the model range in that series.