You actually screw it in. It actually screws inside the internal rod at an angle. This causes the rod to pull up, thus pushing the lower part of the seatpost, again, up, compressing on the walls.
It actually pulls up just a few millimetres, so you need to screw in the lower part the at right height before putting it into the frame.
That's correct...it's exactly a few mm wider.
Actually I think it's simply a hole, the bolt screws in in the other side of the seatpost, maybe...need to verify :) can't remember correctly. But that's the general idea.
You actually screw it in. It actually screws inside the internal rod at an angle. This causes the rod to pull up, thus pushing the lower part of the seatpost, again, up, compressing on the walls.
It actually pulls up just a few millimetres, so you need to screw in the lower part the at right height before putting it into the frame.