I have the Fusion .012 dia (24 lb. test) and it works well. But I think you'd be perfectly fine with the smallest--.004 (10 lb. test) for 1/2 A planes. A quick look at the AMA website for C/L guidelines indicates that, at worst, you need to multiply the weight of the model by 4, and each line should be able to withstand a pull of that amount. I doubt that you have a 1/2 A plane that weighs 2.5 lbs, so I'd say the small stuff will be good!

Here is a link to Spiderwire's website for the Fusion product:
[link=http://www.fishspiderwire.com/NonFlash/Products/LineDetail.cfm?ID=4]http://www.fishspiderwire.com/NonFlash/Products/LineDetail.cfm?ID=4[/link]

Good luck,

Phil

Edited to correct the size indicated.