With two of these you can mount umbrellas with a cylindrical main shafts onto your balcony railing. The railing has two have two or more horizontal rectangular bars whichs inside edges line up vertically. Rubber inlets prevents the holders from slipping sidewards and ledges prevent them from slipping downwards. To mount an umberlla: First put one holder on the topmost rectangular bar where you like it. Fixate it with two velcro-tapes. Then mount a second holder directly below the first one onto the lowest rectangular bar. Finally slide your umbrella in and fixate the hight with the hex bolts and wing nuts. An added set of simple size adapters can make this work for a wide diameter range. Features: First posted here: http://www.quirky.com/ideations/510894You'll need: Then: