This coupler will connect 2" Schedule 40 PVC to a 2" Shop Vac hose. Given both of these are 2" ID but they have considerable different outside diameters, a coupler solves the problem. The 2" Shop Vac hose I have (and I have seen) have a soft rubber ring, which fits snugly in the smaller end of this coupler, which is slightly tapered. The PVC side is also tapered to snug fit the Schedule 40 PVC; once a desired fit is obtained, you can glue this in place with some sort of epoxy.