I have 4-40 control rods and Dubro threaded ends that I'm trying to solder and I can't get the solder to stick. I'm using flux and silver solder with a small torch. The metal just won't take the older. I heat it up plenty, and use flux on the joint, but the solder just drips off.
There's gobs of it on my basement floor.

I solder electrical very well and I know something is very wrong here. Is 4-40 control rod and the Dubro control rod ends solderable?
Do I have to sand down the control rod first?

Thanks,
Joe