[joebob]

Not sure of the exact size but Aloft Hobbies carries metric size ones that I'm sure you could use. I got the 12mm ones to use in place of 1/2" and they work out fine.

 

[joebob]

Shipping is almost twice as much as a tube. Better order a bunch of them to spread it out. 5 would run you $135 delivered. The 12mm ones from Aloft would only be $73 delivered. Something to consider....