Well I've taken some pics but the forum won't let me post them for some strange reason. The single wire just has a normal loop on the model end. It's pushed down the wing cavity and the loop goes over the bobbin.

You can buy solid steel control line wire from Mervin at: MBS Model Supply

The minimum wire diameter for monoline for your class of model is in the C/L Speed rules published by the AMA. Here in OZ it's .016" for .29 powered models.

The stuff for US Speed flyers is available via the North American Speed Society at: https://clspeed.org/

I'll see if I can work out why I can't post pics.

Ray