Exhaust diameters and joining and things

[Tom]

Right guys i've ordered a 2.5inch 90degree bend to replace my exhaust elbow and a flexi to go onto that but now i need a piece that goes onto the flexi to join to my current downpipe, im pretty sure its just stock de cat pipe, but i cant get under to measure it. My plan is to get one of the connectors i have linked below but ask for it to be a welded join one side to join to my flexi then the other side a clamp on fitting to secure to my original downpipe after i chop a bit off. But i dont know what size to ask for with this clamp on connector, anyone help? Or even suggest a better idea if you have one? Cheers

edit: link lol http://www.ebay.co.uk/itm/Exhaust-Adapte...3367b8ffb3