The factory numbers don't match for the hubs.
Here is my measurements taken from a 06 KX450F
Hub is stamped: 0003-1 or 0003-2 -
25MM AXLE DIA -
BRG TO BRG 133.5MM -
ROTOR OD 240MM -
ROTOR BC 4 ON 133MM -
SPROCKET BC 6 ON 150MM -
Factory says it FITS 03-05 KX125, KX250, 04-06 KX250F, 06 KX450F.
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Here is my measurements taken from a 07 KX450F
Stamped: PFD - 0025 -
AXLE OD 25MM -
BRG TO BRG 133MM -
ROTOR OD 240MM -
ROTOR BC 4 ON 133MM -
SPROCKET BC 6 ON 150MM
Factory says it FITS 07-08 KX250F KX450F
So, my bet is they will interchange but I have never tried it.
However, the rim width is narrower on the 250F.
RIM,RR,1.85X19,BLACK 2009 KX250W9F KX250F
RIM,RR,2.15X19 2006 KX450D6F KX450F