It is ment to be stuck into the hose. In my case, the hose had an outer diameter of 40 mm and an inner of 32 mm. I put some hot glue into the hose before pushing the adapter in. Make sure the glue does not obstruct the air flow.
Works fine for a Dyson V7 etc. with this adapter:
https://www.printables.com/model/345472-dyson_v7_v8_v10_adapter-with-inner-diameter-41mm
Nozzles:
https://www.printables.com/model/307565-parametric-vacuum-nozzles
The author marked this model as their own original creation.