That's a 40 mm adapter to fit a 203 mm rotor on forks with minimum 160 mm rotors - do some research on your forks. If they have minimum rotor diameter of 180 mm instead of the old 160 mm , then you just need a 20 mm adapter .
I also bought new pads ( after replacing fox 34's with 36's , wondering why the brakes were so cr@ppy down the first black run, and then having the front wheel locked when I got back to the carpark.....)