Originally Posted by ViperZ
OK, understood. 20mm is the Axle Diameter? If it's not 20mm then what is it?
So do different size rotors require different sized calipers, or are calipers ones size fits all?
a 20mm axle is a 20mm diameter thru-axle, not a typical quick release axle (so yes)
And for different size rotors the calipers themselves are the same, but the adapters that connect the calipers to the frame/fork are different. If you buy a brake with a 180mm rotor, for example, it should come with everything you need to install it on your frame's/fork's mounts.