I'm not really privy to the part number scheme by Honda.
From looking at numbers for different years of RC51 and other bikes, it seems the 1st sequence is the main part, the 2nd sequence has to do with model year or variation of the part, and the 3rd sequence is yearly or minor variations of that model.
Honda is known to use the same part on many different model bikes.
The front calipers are the same as on the CBR600F4I (except in black). The front brake master cylinder is frequently used, etc.
If a part is used across model lines, you'll see a variation in the 2nd sequence.
For instance, the radial master cylinder for the '04 CBR1000RR (PN 45510-MEL-006) is the same as the '09 CBR1000RR (PN 45510-MFL-006).
What's the difference between the MEL and the MFL in the 2nd sequence? Different reservoir design.
The '04 uses a reservoir cap with two screws (same as RC51) while the '09 reservoir cap screws on.
That's how I came to use the parts listings from MrCycles for my research.
They sort the numbers out for that specific year, as opposed to the other sites that lump all the numbers together and have you sort them out.
Came in real handy when I was ordering bodywork and wiring harnesses for my '02.
Last edited by SubSailor; 12-15-2009 at 10:22 PM.