Bicycle Mechanics - campy ergo derailleur housing diameter?

I'm about to replace this stuff on a build. I've come across 4 and 5mm outer? Which is the correct size?

Also, I noticed that the lever body has a fork in the routing for the derailleurs to go towards the front of the tops of the bars or along the rear of the tops? Whats that all about? Flat top modern carbon bars?

If the ergo levers are pre-2009, then the cable housing diameter does not matter. A ferrule is used at the ergo lever and all ferrules should have the same outside diameter. I would suggest using 4mm housings and of course you need Campy compatible cables.

Ergo levers have the the option of routing the shift cable to the front or around the back of the bar. With the older models, you might find that the back routing creates contact between your palm and the shift cable. With the front routing, the cable housing crosses over the top of the ergo lever. If the cable falls along the crease in your palm it may not be cause, but it certainly can. I always use fiberglass reinforced strapping tape to hold the housing down firmly and then place some foam rubber tape like camper seal beside the housing to smooth the transition onto the bar. If you bars have one cable groove along the front, place the shift cable in the groove and the brake cable below it.

The new 2009 levers have eliminated these cable housing issues. Campy has new 4.1mm ultra low friction housings for the new ultrashift levers. Shimano 4mm housing will also work, but not all 4mm housing have low enough friction.

excellent! Thank you!