Originally Posted by
123123user
I bought a bike at a lower price and it seems that some parts aren't Shimano-branded like its sprocket and derailleurs. I plan to buy the better parts so I can replace the generic ones. Can I just get that spare part and use it in the bike, or does it need to be compatible and the same with the already Shimano parts? I would try to look for any shimano derailleur according to bike transmission.
Hard for me to understand your question(s) from what you have written.
I think you are asking if the drive train, i.e., shifter, chain rings, rear gear cluster (freewheel or cassette) needs to match or all be from the same group.
If you are using index shifters, the answer is
generally yes but not always. If you are using friction shifters you have a much betteer chance of everything working properly.
You need to be more specific about your request: what bike, what components (model nos./name). Shimano makes an incredibly large array of components for everything from wally world bikes to high end bikes.