Could it be half a door knob. I had brass door knobs with a metal bar that went through the hole. One knob with attached bar was poked through hole and screwed into the knob on the other side.
Heck, all this talk about screws, knobs and holes, I'm feeling quite light headed.
Humankind has not woven the web of life. We are but one thread within it. Whatever we do to the web, we do to ourselves. All things are bound together. All things connect.