85mm roof air vent

[DIYspanner]

The spout on the roof's air vent is 85mm o/d which is 10mm smaller than the i/d of this type of duct bend.

Are there adapters available?

Seems daft that the the roof vent spout is a reduced size.

The house is a 2003/04 build.

 

[robinbanks]

Going to be fairly low pressure though, if push comes to shove a 7mm or so foam tape that is slightly compressible will form an adapter between those two diameters