When I ordered the kit (from seller "Fisters" on amazon), they asked me to measure max travel in x/y/z.
They take the travel and add a fixed amount to cover the read head. (140mm added to each scale)
I sent them the following e-mail:
Good Day,
My mill is a Rong Fu 30 clone, and the travel that I measure is:
x: 510mm
y: 184mm
Z: 130mm
Thank you,
-Tom