Fitting a 3" Cat back stainless exhaust to a standard Cat

[g60leigh]

Has anyone here fitted a 3" exhaust system to the standard S3 catalytic converter is it a straight bolt on or will I need to get either a reducer or a piece of sleeving?
(What is the standard system diameter?)

thanks

 

[vetch]

I thought I'd give this a bump as Id be interested to know the answer too.