Just looks like part of a lockable door knob to me. I guess I should say the outside part where the key goes, lol. The part that you turn with your hand seems to be missing, but that looks very much like a keyhole in the center.
I don't think its a part of anything. The penny shows the size of it and you're right about that being a keyhole. I believe turning the key would cause the ball to come in half, just don't see the purpose.
Identified. I showed it to some old guys at the local coffee klatch and one of them knew what it was. He said a key would take it in half then you take a lug nut off a car wheel and put the ball half on it. You put the lug nut on and tighten it then put the locking part back on & lock it . It makes the wheel theftproof. Makes sense to me, wish I had a key for it.
They never said you tighten the lug nut with this. You unlock the "door nob" and it comes in half, before you tighten the lug nut, you place the back half on the stud then use the lug wrench to tighten the nut, then lock the other half over it. Although it may be a good deterrent, I would think that it may throw the wheel out of balance.
I have a model A ford and I took a wheel nut off to see if the ball would fit the stud and it does. The nut is too big to go through the hole. If you put the ball over the stud and tighten the nut down in it, then the locking part could be put on. I don't have a key for it but I would be concerned about imbalance even though cruise of the A is only 50mph.