The lovely VO bottle cage mount allows you to affix water bottle cages on your handlebars. They are made of extruded aluminium and are intended for city bikes, so they fit bars up to 25.4mm.
(I know some of will want to use them on the 26mm "sleeved" road bars. In that case you'll need to file just a touch off the top edge of the "hinge" section so it opens a liitle wider. Of course, it's no problem to use them on "bulged" road bars.)