Are there any elements that can be connected to the 'cavity' (i.e. the space) under a stud (e.g. on a regular plate or a regular brick)? The cavity measures about 2.4mm in diameter.
So far I've only tried a minifig hand peg (not the clip side, the other side) but unfortunately it is just a bit smaller, it has a diameter of about 2.3mm.
[Edit] I'm talking about the cylindrical cavity with a diameter of 1.5 LU as indicated in the overview posted here -- What are the dimensions of a LEGO brick?.