What type of nail is this?

[simulant]

 

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[old digger]

Looks like the wick control to a oil lamp.

 

[simulant]

Looks like you nailed it! Even though it's not really a nail.

Here's a pic that seems to match what I have:

 

[Dug]

Agreed

Looks like the wick control to a oil lamp.

Agreed.

You will likely find a maker's name and or patent date on the face of the knob if you clean it carefully.