4" Dust collector to 2 1/8" Shop Vac hose reducer.

One end fits inside a 4" dust collection hose and the other side is big enough for a shop vac hose to plug into it. Dimensions are close enough to not need a clamp, but i put a ridge around the large end in case it needed it. I used metric measurements to create what I needed, so it might not be exactly 4" and 2 1/8".