HANDY TIP:
The tubing is sized by ID (inner diameter). If you only know the flat width of the tube size you need (measuring across a flattened tube), but aren't sure what ID you should choose, you can quickly approximate diameter by dividing by 1.6! For example: If you need a tube that is 3 inches wide when flattened, you would divide 3" by 1.6, which equals 1.875". That means you should order the 2" ID tube