Alex: I do not know how the originals were made, but you have a two-piece effort there, so they need to be joined. file and fit the surfaces of the stem to match the socket as close as you possibly can, in the concave junction and on the outside of the piece, flux, and joint with high temp silver solder. that requires red heat, so an oxy/acetylene torch or the like, will be needed. You'll also need a fixture of some sort to hold everything in alignment during the join too. The closer you can make the fix, the less of a joint you'll see. Done properly, it'll be as strong as if one piece of steel.