1999 900 carb vacuum hose size

[Autostrada Pilot]

I bought some new vacuum lines to replace the 2 coming out the bottom of my carbs that were cracked.  I'm talking about the 2 that drop out the bottom of the carbs and connect at a "Y" and then drop down by your right foot to vent.

Previous owner used too small, and super-stretched the line to fit the nipple, but the super-stretch is why they are cracked and breaking.  I tried the 1/4" fuel line I am about to replace, and it was too big.  What size would work best for a good fit.  I am still using the factory Mikunis (damn you, FCR's, for being so expensive!).