Direct Info from Product Website : https://www.co2art.us/collections/co2-accessories/products/u-shape-glass-co2-tubing-connector

New U-Shaped Stainless Steel U-Bend Tubing Connector

• Made 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 2 different sizes:

• Small: For tanks with 0.4 inch thick glass
• Medium: For tanks with 0.6 inch thick glass
• Large: For tanks with 0.8 inch thick glass