Downpipe to standard Cat

[6.5ghost]

To join a 3" downpipe to standard Cat, what gasket 3" or 2.5" will it need

 

[B6lee]

To join a 3" downpipe to standard Cat, what gasket 3" or 2.5" will it need

surly a de-cat is more essential than a downpipe

 

[Ozy]

+1 decat then a downpipe

 

[6.5ghost]

I know, but the pipe is blowing. MOT is due, want to change pipe to get through the MOT, then decat.
Standard downpipe on the car now, it seem's more reasons to have a 3". Just not sure what gasket to use at connection to CAT.