Confused with cooker hood venting

[Fordy81]

So I've put my parents in a new integrated cooker hood. The outlet is 120mm in diameter. Most kits seem to come in 125mm. Am I ok using that with a hose clip to clamp it down? Also I need a backdraught shutter. Will a 125mm fit? Is the 125mm the internal diameter, or the external?

Thanks

 

[endecotp]

I suspect that internal vs. external diameter is the reason for the different diameters that you're seeing. If you have something with a 120mm external diameter, then that is supposed to fit inside whatever it connects to.