Working diameter of the front brake cylinder

[LuckyTriumph]

Does anyone know what is the working diameter of the front brake cylinder? I tried to measure myself, but I just can't do it without disassembling the whole system.

 

[chevaliernoir]

When I asked myself the question, I realized that :
- KTM does not provide any maintenance kit for the master cylinder
- the complete assembly is very cheap

 

[Foolishboy]

whatever it is its crap, Ive used the master from a 2009 zx6r which is a 17mm piston i think and after one track day was very impressed, brakes actually feel solid without feeling wooden, didnt have any fade all day like I usually do.
All i needed was a different banjo bolt to make it work.