If you look inside the empty wheel cavity (the wheel cavity is the hole on the bottom of the shoe where you normally insert your wheel and/or plugs), you'll find the type and size of wheel/plug that your shoe uses imprinted inside the wheel cavity. For example, if it reads 'FATS-L (US 9-12)', you will need to order FATS wheels and/or plugs in a size LARGE, which fits shoes in US sizes 9 through 12. Please note: If the imprint only shows a size (Small, Medium or Large), you will need the FATS style in the stated size.