Exhaust question

[Nima]

I was reading a few threads about exhaust systems and after market brands when I came across this question (although exhaust update is not my first priority for now). Are these after market bolts on exhaust systems really bolted on or do you need to do some welding? For example, welding the muffler or adjusting the length of the tube? The reason I'm asking is I don't have any welding equipment and experience.
Thanks for the tips. I wish a good weekend for everybody.