Over- hob extractor - what are the standard diameter(s) for the ducting?

Just nearing the end of a kitchen refurb. Tried to fit the extractor (a CST61) but the spigot for connecting to the ducting system is 115/118mm diameter (bendy plastic!). This doesn't seem to match either of the two standard diameters you can get from Screwfix (100mm or 125mm) although I haven't actually tried either of these two sizes yet). Does this seem like a non-standard size or is it a standard size that Screwfix doesn't sell?

Thanks for any comments from the experts.

diymostthings

 

OK CGN Thanks. I'll give that a try.

diymostthings

 

OK CGN - no need for a photo - your advice worked absolutely perfectly and I'm delighted. Thank you so much (again!). For the record I asked for advice over the counter at a well known merchant (not Screwfix or TS) and he told me utter rubbish! Thank goodness for this forum.

diymostthings

 

Thanks Phil - well that would have been handy but CGN's advice worked fine. Will bear that adaptor in mind for the next job.

diymostthings