The whole clutch? Each fly wheel is a lil bit differant, each manufacturer has a branded model, some are better quality, and yes there are differant spings, if you have a bunch of used ones, or ones you think are use, if you can afford to toss em out, just get one or two new sets, around the 1.0 range is a good starting point, Mugen, Kyosho, Jammin/Ofna stuff pretty much are interchangable, you will most likley need to make mesh adjustments if have different brand stuff, but they will work fine together. The AE and Losi stuff is not really interchangable with other brands, they have bigger bearings (At least I think AE does? Losi for sure) the biggest thing you need to look at in my opinion is the flywheel diamater, not sure what you have, but if you change up make sure you do not go bigger, your buggy will stall if you case a jump, or even land hard sometimes, just make sure it is not sticking through the chasis, once springs get all mixed up its hard to tell what each one is exactly..least for me it is, I keep a few used ones just in case, but try to always run known good ones, and change them every three or four races, same with the clutch bearings, they take alot of heat and abuse...Hope this helps a bit.