I made sure I got the right size for a fox 38 180 post mount to 203mm rotor. On the website it will the 23mm size adaptor. 180+23=203, makes sense. When it came it's well designed and has a great look but IMO it pushes the brake calliper too far out and the pads do not contact all of the rotor. I put on a new rotor and pads, so I can see where the wear is starting and it's definitely not contacting all the braking area of the rotor. Still, I'm stopping well so I'm going to see how it goes, maybe I'm wrong.
23mm / Gold