Horn button

[c. ladouceur (RIP)]

It would appear if there are two styles of panels, then there are likely two different buttons. One seems to mount on the surface,(both of mine are like that-no large hole between the screws),and one mounts through the panel-with the screws going back through the panel and screwing into the button base.
Does anyone know if this is so? Maybe the large centre hole was drilled only if a horn was actually mounted?