I have been looking around to stock up on cable housing. I like to keep spare parts around.

I see 4mm and 5mm housing. I see lined and unlined. I see some are "non indexed".

I assume that 4mm is for shift cables and 5mm for brake cables. Right?

Advantages to lined cable are? "non indexed" cable housing means????

Any specific recommendations for brands and or types would be appreciated.
Thanks