We've recently released our Universal Adjustable Planter Box Brackets and they are getting 5 star reviews on Amazon, Wayfair and our site! They can be purchased with our 20" or 36" mounting rails, or if you already have one - as a set! The 20" rails will hold up to a 30" long box, the bottom (width front to back) from 5.5" to 8.5"accommodating most tray style planter boxes! For longer boxes, choose the 36" kit. All will hold up to 35 lbs when installed correctly, which is super easy! See our instruction page for what our kits will fit on - most vertical spindles - and how to connect without damaging your railing!!