Assume you try it.
Even on a 1/2 dia (12 mm) threaded rod, the minor diameter of the rod is your strength limit, right?
Run a weld bead around that minor diameter, and you end up with what is actually a very, very short fillet weld of only .417 inch x 3.14 = 1.3 inch long, but the weld quality is very, very low. Fusion of start and end point is troublesome also.
Tensile stress area of the 1/2 threaded rod is only 0.142 sq inches.
Weld fusion is very questionable because of thread dirt and crud trapped in the thread depths.
If you grind off the threads to get a barely adequate weld surface, you tend to cut into the minor diameter, so you net weld area is even smaller and final minor diameter of the rod is even less.
Fillet welds are only qualified for the "leg" as high as the material thickness, but that is a valid thumb rule for long "straight" welds of two equal (or near-equal) thicknesses of base metal. Here, you might have a weld leg equal to (or substantially less than) the flat plate thickness, but the rod "equivalent thickness" is NOT 1/4 inch (the radius of half the major diameter), and not even half of the "minor diameter" radius (half of 0.417 or .208 inch leg) because the fillet weld is wrapping around the rod's core. So you end up with a wrapped fillet of maximum credible "leg" height of about 0.16 inch tall ... Barely better than a tack weld in yield strength.
