The Campy Delta works by pushing a cam like device from underneath. I believe it has metal to metal contact too. A centerpull pulls the 2 arms closer by drawing them closer upward toward a fixed cable attachment point. This is a small difference but I believe the other suggestions were perhaps of an exposed centerpull with an integral fixed cable attachment point. This would leave out Shimano AX but I think the others that were mentioned still qualify. Something about a Weinman Vanquerer with an integral attachment seems so elegant that it appeared in my dreams several times during my flu induced delirium.
Garth Libre in Miami Fl.