An actual duct that will fit a 127mm hole

[Sprogginz]

I want to buy this
http://www.screwfix.com/p/erbauer-diamond-core-drill-bit-127mm-x-150mm/99629
to fit a vent for a cooker hood extractor and was going to buy something like this
http://www.screwfix.com/p/manrose-cooker-hood-kit-125mm/17489
because it's 125mm so should fit in a 127mm hole right?

But reviewers are stating it's not 125mm but larger and I've found a lot of other products like this too.

Can anyone actually point me to some products where they know will go into a 127mm hole for an extractor that is for 125mm ducting so that I don't find myself scratching my head?

Thanks very much and hope you can help.

 

[kazuya]

if you read the reviews for the cooker hood kit, someone says "The erbauer 127mm core drill is perfect for the job if used with the plastic tube - the metal flexi-tube will not fit."

 

[Sprogginz]

Thanks for your reply.
I read that so basically there's no point buying this kit but buy separate items instead?
I can see a plastic tube on Screwfix with a 125mm external diameter but 350mm in length, so would the length be still fine for a double cavity wall?
Thanks again.

 

[kazuya]

yea 350mm will be long enough to go through a cavity wall