Gtk.Settings:gtk-icon-sizes

"gtk-icon-sizes"             String                : Read / Write

A list of icon sizes. The list is separated by colons, and item has the form:

<replaceable>size-name</replaceable> = <replaceable>width</replaceable> , <replaceable>height</replaceable>

E.g. "gtk-menu=16,16:gtk-button=20,20:gtk-dialog=48,48". GTK+ itself use the following named icon sizes: gtk-menu, gtk-button, gtk-small-toolbar, gtk-large-toolbar, gtk-dnd, gtk-dialog. Applications can register their own named icon sizes with Gtk.icon_size_register.