New U-Shaped Stainless Steel U-Bend Tubing ConnectorMade of high-quality Stainless Steel. U Shape for Co2 System. Provide nice alignment for tubing goes over the glass edge from outside to the inside of the tank. For 4/6mm tubing.In 3 different sizes:Small: For aquarium with 1cm thick glassMedium: For aquarium with 1.5cm thick glassLarge: For aquarium with 2cm thick glass