Thats a 2mm walled tube, a bit thinner than the stuff ive used. a good thick wall lets it bend without kinking and it wont collapse on itself with negative pressure..
once upon a time a member in here sold suitable 1/2" silicone tube..
there is silicone and silicone. i wouldnt use the stuff sold for automotive use for example..
some brewshops sell the stuff that is food and heat safe for our use
http://www.themaltmiller.co.uk/index.php?_a=viewProd&productId=352
im no expert but think that if looking outside homebrew suppliers if you source the platinum cured tube as used for milk transport in dairy use you wont go wrong.