The converter on the left has an anti-balloon plate added, while the one on on the right has a stock-style cover. The plate helps the converter resist flexing and expansion in the thin hub area under extreme conditions. These plates come in various diameters and thicknesses depending on the application and are recommended for high-horsepower applications, especially with a power-adder like N.O.S. or forced induction. Phoenix uses antiballoon plates on all of its 245mm converters.