These unions are used to join lengths of aluminium gutter together by placing the union into the rear face of the gutter and clipping it down at the front. Each aluminium union features two large holes on its base, which are to be filled with sealant during the installation of aluminium gutters until it reaches smaller holes at the rim of the union.When joining aluminium gutter lengths to unions and other fittings, the process must be completed by injecting ARPand#039;s unique 3923 sealant after said fittings have been clipped into position in order to ensure a secure fit.For a full demonstration on how a union is joined to other aluminium gutter components, check out our aluminium union jointing tutorial video.One aluminium gutter union is supplied with every aluminium gutter length, running outlet and angle free of charge.