I commend your weld fabrication of similar.

I recognize the bolt from my childhood cheap and vintage bikes, some of my bikes had that projection all the way across to the other side I think. But come to think of it, I don't have a single bike now with that feature, either the frame is female threaded or insert-nut on the left side into a hex hole for bolt entering on the right, or no bolt and they use a "turtleneck" top, either quick-release or with bolt.