Can you identify this modified 1x1 plate?
It's appears to be either Part 4081a or Part 4081b.
I'm not sure if it is exactly the same, but this works as a starting point, I believe. The two linked pieces seem to differ only in the thickness of the ring of the added &quot;limb&quot;.
I was unable to find a part like those that has a &quot;hole&quot; in the main stud.