why don't you take your 4" hose and a piece of 2 1/2" to a box store and get what you need their ? that is what i did good luck you may get a furnco which is a brand name which is a rubber type of coupling which would be ok for that useWhat seemed simple in ordering may not be.
Router table says is has a 2 1/2 inch dust port opening.
I will be going from a 4 inch hose to this.
Do I order the 4-2 1/2 reducer or are these going to bump rather than fit over.