This was mentioned in another thread, and I'm not sure the one in the first photo is correct. The second one is what I have just received from st John street cycles - a campagnolo seat pin.
Now I have it I can see how it works - there is a none-threaded bit on either side that fits snugly in the holes of the seat clamp. Instead of exerting force from just the outside and bending the clamp inwards, it encourages a parallel drawing together of the two sides. The internal, snug-fitting threadless bits don't allow pivoting.
Just my observations. Sjs was the only place that had them - about 9 quid.
Sam