Ferrules are used to connect the sanitary process lines to the union. These come in short, medium and long. The Metal Company have both Expansion or otherwise known as Slip On Ferrules and Butt Weld Ferrules.
Tri Clover Expansion Ferrules have ridges on the inside and slip over the tube. These require just one weld to create a hygienic join. While Butt Weld Ferrules are typically purge welded for hygienic applications.