They are made to accommodate 15mm ID pipe, which seems to be a readily available size.
The cross in the middle is for structure/strength and the cross-members are 2mm in width. These can be done to any shape or design or angled to direct flow.
I also don't want to scavenge too much air away from demisting the windscreen, that is the really important bit. I thought I might need to choke them off a bit more, if anything, to stop too much air coming out.
I'll be poking around in the dash of my Landy in about a week and will come up with final design at that point. I need to see if the in-line pieces will fit in the space under the dash, if any angle to the vent is required, and a few other finishing touches.
Now what about the ash tray? What can I print to go in that space? Someone has already come up with a simple coin/key tray, I might see if I can convert it to a phone holder/charging pod, or a gauge pod, cup holder,
