Industrial Gutter Unions, sometimes referred to as joiners, are used to connect two lengths of gutter together in a run.Gutter is clipped in place using the same method was when installing all gutter fittings - the back edge first, then pull the front edge gently down into position until the clip snaps into place. Inside the gutter union are insertion marks, which show exactly where the gutter should be positioned. Aligning the gutter to these marks ensures that as the gutter expands and contracts with changes in temperature, the seal still makes full contact with the gutter.The waterproof seal is achieved by the downward pressure of the clips compressing the small rubber seal evenly around the outside of the gutter. We recommend the use of SL40 silicon spray on all seals when installing our XtraFlo Industrial gutter.Unions are fixed back to the fascia board using two countersunk screws.