Join the club of guys with a box full of 4 inch connectors that are mismatched and NOT 4 inches. I finally just stick with the Rockler Dust Right stuff, which seems to fit. The part with the nahdle fits (see pix lower right) over dust outlets on your tools. It stays attached to the hose. Ocasionally I have to wrap a little tape around the male connector to get a tight fit.
Going from small hose to 4 inch, I found connectors that have both the small hose size (2.5 inch and 35mm), and a 4 inch male connector (Pix, lower left). That connector just drop into the female connector with the handle. Suction holds it in place.
Pull the handle connector off, push it on. Easy, fast. I have a right angle connector with the rubber gasket you tighten up on the out flow connector on the router table. Just long enough so I can slip the handle/connector on and still keep the table near the wall. I have a little bracket to support the extra weight(upper left).
Frustrating to buy stuff that says 4 inch, but isn't. Wish they give the inside and outside diameter so you''d have half a chance to get it right the first time. So I stick with Rockler. One accessory I have come to appreciate is a 3-foot length of 4 inch tube with a floor sweeping attachment (not shown). Slip the handle/connector on the other end and you can really suck up the sawdust.
The last item is a 4 inch to 2.5 inch Y connector that facilitates air flow.
Rockler also has a set of connectors you use in a chip collection system. And they have a swivel connector which I put on the input side of the collector so the long hose won't bind.