Spiral ducting for domestic 150mm cooker hood

[notreadyforthis]

I've got a Siemens cooker hood which has a 150mm vent and it recommends a rigid venting system for optimum performance and reduced noise.

 

I got what I thought would be a simple push fit elbow, pipe and external grille which do indeed fit together nicely. But none of it fits the cooker hood, they're all of the exact same diameter.

 

What am I missing here, some sort of connector or coupler? I posted in another forum and they said I can't use spiral ducting for a domestic cooker hood as it's designed for industrial systems.

[Bonner]

I would use rigid plastic stuff, cheaper, easier to work with and probably quieter. If it’s the same size as the bend, try the pipe directly onto the spigot.