Meaning of final letter in Audi part number?

I have two part numbers: 8DO601025M and 8DO601025B, both referring to 15" alloy wheels. The only difference between the two is the final letter. Can anyone
please explain the significance?
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8D0 601 025M is for 6Jx15 H2 ET45 5/112 alloy wheels. Mounted on A4, A6 from 1998-2001 8D0 601 025B is for 7Jx15 H2 ET45 5/112 alloy wheels. Mounted on A4, A6 from 1995-1997
Peter Thorn a crit:

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nom wrote:

Thanks. That's odd, though. Someone is advertising the "M" part on ebay.co.uk as a 7J x 15H2 ET45 (item number 4618251311).

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