Which size is for a diesel one mate ?!As Hicky says it slides over the existing exhaust and than fastens in place by a screw...very simple.
I got one from my local dealer for about £33.. I think it looks much better than the standard black metal one..
Just be careful as there are two sizes....one for diesel and different size for petrol..
I would suggest, at that price, you buy from a dealer...to be sure you get the right one..