Exhaust Donut

[Vic]

I am designing my own 4-1 headers and exhaust system. Can someone please give some info about what an exhaust donut is, it's function and how and where it is to be used. I think this posting might sound vague to some people, but I need to ask.

Here's all the info that I found on the catalog:

Exhaust donut (2 inch)
The best way of adapting your turbo muffler to the header. These full circle donuts have a radius equal to the tube diameter. This allows you to keep the pipework required to a minimum and makes for a super neat installation. One donut is sufficient per system.

[CptanPanic2]

I believe it is a way to step pipe diameter differences. For example it would be an easy way to mate a 1 5/8 in pipe into a 2 1/2 in muffer. I think that is right.

[Vic]

Thanks Captain, thought somethong similar, but thought it better to have a second opinion.