my back box outlet pipes are 50mm (2") OD , and that should be the same for all the 2.0tfsi Quattro's and 2wd variants ,well if you have original OEM setup still fitted that is.
I have not measured the outlets on diesel setups so cannot confrim what dia pipework they use but the installation method should be the same.
The tips I went with have a inlet of 50mm OD to 60mm OD which was a bit tight to slide over my 50mm outlets ,well it woud'nt go full stop so went with a reducer and cut of the 50mm section on the tips and slid the reducer into the 60mm section then welded it in place, that way I got the right overall length I wanted and the tips then slid over my exisisting pipework and welded on. job done, well that's the short install version.
Here is a bit more of my install from my older thread, sorry if it's old news but thought it may help here now aswell.
" 2 options available here, first and the prefered method of attachment is weld-on as its a stronger fixing method if fitting a heavier tip also does look better than a clamp, 2nd method is to just clamp them on to your back box outlet, if going this route you will need either a staight coupling that fits over your exisiting
OD pipework or a reducer and then over your selected tip pipe, plenty of straight couplings to be had all over the place, most have clamps included.
Some sellers will slit your tips to facilitate fitting over your back box outlet aswell, same applies really that you need to ensure you have worked out your OD & ID sizes in advance to make sure it all fits together properly, it sounds harder than it really is to be honest, just require a bit of forward planning that way it will look spot on.
I am a reasonable welder so opted to mig weld mine on, so purchased a pair of 2" stainless steel straight reducers and have today welded them onto the tips and then polished them up with my polishing mops kit on the bench grinder, they look spot on now and match the tips nicely.
just need to lop of the old tips and get the pipe to the right lenght then weld the tips onto the pipework.
may do it on the car or may whip of each back box section and fit them that way to make sure they all fit spot on.
like i say, sounds like a lot of work , but in reality its not.
there is a 3rd option and thats to get them fitted for you, but you'll pay a bit abit more, choice is yours .
What you need to keep in mind with all these tips is the tube diameters, a tip with a 50mm OD fitting wont just slide on to your 50mm OD outlet pipe work, you'll need to either use straight couplings or reducers , worse case maybe slit your new tips and force them on but that's not really ideal frankly, reducers/coupling are not expensive and wether you weld or clamp the tips on as long as you make the connections a nice snug fit and tighten up well they will be fine.
hope that has been of some assistance.
rob