I purchased one of those slip on exhaust off of Amazon and when I received it it came with the muffler a 5 inch adapter piece because it's Universal and some welding is required has anyone ever bought a slip on exhaust system like this for a 2000 CBR 600 f4

 

"Universal" typically means modifications will be required before it fits any bike in the universe. (rimshot)

Not sure what product you're talking about but the last off-brand mufflers I bought came with this:
https://www.amazon.com/Emgo-Muffler-Reducer-80-47310-1/dp/B00230CC0G/ref=asc_df_B00230CC0G/?tag=hyprod-20&linkCode=df0&hvadid=312455765168&hvpos=1o1&hvne tw=g&hvrand=5095686291728714271&hvpone=&hvptwo=&hv qmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9007307& hvtargid=pla-570063719209&psc=1