Don't take flat rate boxes.
Instead, for small and medium items, choose "First Class International Service".
Very small items go for about $8-$10
Stems, Seatposts and such go for about $11-$20
Bars / Bar-Stem-Combos and other things, if not too long/wide, go for a little more.
See here for an example (shipping sth. of 300g incl. wrapping to Austria): http://ircalc.usps.com/MailServices.asp ... c=4&dv=20#
There it says:
First-Class Package International Service™
Maximum Value for Contents: $400.00
Other than rolls: Max. length 24", max length, height and depth (thickness) combined 36"
Rolls: Max. length 36". Max length and twice the diameter combined 42"
Risk is all the buyer's. Description says there's no tracking, which is not entirely right. Every letter/parcel gets a shipping nr. with which one can follow the shipments way inside the US borders. So one can see when and where it was posted and when and where it leaves the US. That way there's no risk for the seller.
Sometimes it takes 2-3 weeks, longest I have ever waited is 5 or 6 weeks (don't remember exactly anymore), but so far nothing's been lost (knock-on-wood).