Gutter unions are used to join individual lengths of gutter together. A 2mm expansion gap should be left between each length.With this supported union there is no need for a fascia bracket on either side on the union - instead the union itself is screwed to the fascia board.The supported union uses a key clamp method to lock the gutter in place. The key is inserted into the hole on the tab and pulled downwards towards to lock the gutter onto the seal.