The inch and five eigths dimension is to make baffles that sleeve inside one and three quarter inch pipes. For other sizes using tube an eigth of an inch smaller in diameter is a pretty safe bet, but adjust the size of the drilled baffle tube as well. You can wrap the drilled part in fibreglass roof insulation or similar to shut it up some more. Just dont use anything flammable, or mild steel wool as that tends to burn away as well. The turn over on the fat end is best done with a pair of vise grips a little at a time until you get it to about 45 degrees when you can beat it over with a hammer. Doing it a little at a time helps keep it round so thast it fits into the exhaust pipe when you're done.

The next pic is the way I crimp the end of the drilled tub shut. Make four or five passes at it to avoid distorting the tube too badly. Clearly thin wall exhaust type tube works best...........