round button, square hole?

[deldave]

This is my first flat button with a square hole, hope you all can enlighten me on the subject!

 

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[Broken knee]

It's a wick adjusting wheel from an oil lamp.HH BK

 

[deldave]

trouble is , about the size of a quarter

 

[DCMatt]

It's a wick adjusting wheel from an oil lamp.HH BK

trouble is , about the size of a quarter

No trouble. As BK said, it is a wick raiser knob from an oil lamp.

 

[HuntinDog]

Compare it to a Chinese cash coin.
Although the square hole does look a bit small....
It could be an engraved altered coin.
What does the other side look like??