gtk:toolbar-icon-size (object)

toolbar -- a gtk:toolbar widget
size -- a value of the gtk:icon-size enumeration that stock icons in the toolbar shall have

Accessor of the icon-size slot of the gtk:toolbar class. The gtk:toolbar-icon-size function retrieves the icon size for the toolbar. The (setf gtk:toolbar-icon-size) function sets the size of stock icons in the toolbar.

You can call it both before you add the icons and after they have been added. The size you set will override user preferences for the default icon size. This should only be used for special purpose toolbars, normal application toolbars should respect the user preferences for the size of icons.