Our Junction Tubing comes in 4 diameters; 2.5 mm, 3.2 mm, 4.0 mm and 4.5mm OD. The 2.5mm tubing is mostly used to align free-swinging hooks, or can be used to connect the hook to our 1.8mm tubes. The 3.2mm tubing is used to connect to our metal tubes and our 3mm plastic tubes. The 4.0mm tubing is meant for free swinging connections with our Predator Tubes, or can be tied onto our 3mm tubes for use with bigger hooks. The 4.5mm tubing fits over our Predator Tubes. Our Junction Tubing is made of PVC. PVC does not crack or break like silicone. It comes in a wide variety of colours, including glitter and Glow In the Dark tubing.