Assuming you are coring cans, 2" dia is what you want, and when you cut the end caps off the cans make the cut deep so 2 tabs stick out (inside) the can. This is what you will center the tubing on.
I have a 695, and I've already chopped once and this is the second time (going to do it right this time). I'm not sure about the tabs you are referring to. I measured the existing tube in my can and it was about 1.25". I was going to get 1.5" perf tubing and fab up something to hold it at the outlet end.
Thanks for the links, I'll check them all out. Any others would be great, too.
LAChoppers has it down. Like the price. Thanks for that one!!