Most modern aftermarket rims are made with an oversize center bore and the centering ring brings that bore size down to the Miata 54mm size. These help to properly fit your new alloys. Price is for set of FOUR ALUMINUM rings with retaining clips (picture shows plastic). All our wheels for the new Miata take either a 73mm plastic hub ring or 75mm metal ring (see wheel description to know which you need). These are used in our Enkei RPF1/PF01 15x8 wheels.