Does anyone know what the letter is at the end of the TSM part number?

My 2004 883 has P/N 68920-01C as a part number however I can find several used ones with the same part number except the instead of a C at the end it has a D or B or ??

Can they be interchanged?

 

The letter at the end of the part number indicates a revision change, usually an improvement to the part. The parts should still be compatible, and given the choice, I would choose the "D" over the "B".