ORIGINAL: tubebass
The .012 steel would be too heavy for a 1/2a model, it would be more appropriate for a .15 size model. If you want steel, the .008 size would be correct. I used to use dacron line for 1/2a models, but have recently switched to Spider Wire braided fishing line. It has less drag and is plenty strong.
This is not true. For AMA combat, .012" is required for 1/2 A. This was even the case back before the hot modern engines pushed the length to 42'. .012 is a great size for 1/2 A as it is less fragile. There may be some better materials to use that steel wire now. It seems there is a big push towards Spiderwire, but I am not sure what size. That would be a great material if you can find the right size as it would last a long time.