My iva man didn't measure but did have a good look.
To start with I didn't like the idea of having them in the arches but I think I prefer them now. They are unobtrusive and keeps the scuttle looking clean.
I used
these without the rubber grommet. They are a tight fit but also held in with tiger seal and then in split conduit stuck to the inside of the arch lip.
I also used a pair of
superseal connectors so I can take the arch off if I need to.