Do you mean a master cylinder as used on bikes that have radial mount calipers? I might be wrong but I don't think there is anything revolutionarily different in these master cylinders. I run an entire ZRX front end including their 6 piston calipers and use the master cylinder from a much smaller bike (EX500) as it has a 2 mm smaller diameter piston which was tested to deliver a higher pressure but with less volume to which it produces a very powerful brake that is still highly controllable and feathery when first applied.
