Going down the generic catch can route and have read all the threads relating to catch cans.

As I want to make the visible can end neat using AN fittings fittings I would like to buy everything in advance. If just using barbs/hose clamps at both ends I would simply pull it apart and head to buy the right size hose.

The threads do not seem to quote a consistent hose diameter. I have read that AN10 hose (5/8 - 16mm internal) is a perfect fit to the factory PCV barbs but elsewhere 3/4 hose is referenced.

Can anyone confirm the ID of the hose required to fit the factory PCV barbs?

I recently did mine and used 3/4 silicon hose and it fits perfect on the factory PCV barbs.

I used 1" heater hose from Home Depot, however because I had to get creative in the return route to the PCV, there are more fittings than I'd like, I've noticed Oil dripping from the hoses at the rear of my engine most likely caused by vapor getting past my clamp fittings!!

Just an FYI.
I would reconsider using a silicone hose.
Oil and gasoline acts as a solvent on silicone, essentially dissolving it gradually.