What is it?

 When I was digging a spot for the Northside Bur Oak a few days ago (see that blog entry here), I came across an unusual metal object buried there. When I first pulled it from the ground and brushed it off, I thought it was the top of an old kerosene lamp. A rectangular hole, I thought, held the wick. But there was no hole in the bottom, nor a hole for an adjustment wheel for the wick.

 So that's clearly not what it is. So what is it?

Top View - about 2" in diameter 

Bottom View - there are no openings on the "knob"

 I posted these pictures on my Facebook account and guesses include: a door knob, a wheel cap, part of the handle of a utensil, flag pole holder, part of a door bell, part of an old weed wacker, a holder for a curtain rod, an old cap tap, something that covers the end of a screw or nut, or part of an unidentified toy.

 I'm leaning towards toy. It's very lightweight. And though it's dirty from all the years underground, it is not corroded or rusty. Thus it is not steel. Instead, it is some lightweight metal, probably brass.

 This house has been occupied since the late 19th century, so I am sure many children have lived and played here. I wonder how many years ago it was lost at that spot?

 Your opinion is welcome. How about leaving your guess as a comment?