I used 4mm as its a better more readily availble size.
The actual hose is made from high temperature nylon so i could run it along the strut brace but i realise this is not availble to everyone so silicon taken a
lower temperature route would be fine.
I changed the brass fittings on the gauge to suit the larger pipe and got a 4mm olive too.
The plastic shroud and tee will accept 4mm piping as i have an autometer gauge to and its what i am using