How to measure the tubing diameter of your bike rack
1. Get a pen/pencil, a strip of paper and a measuring tape.
2. Wrap the strip of paper around a section (circumference) of your rack tubing.
3. Mark paper at overlap.
4. Measure from edge of paper to mark and divide by 3,1416.
This will determine your tube diameter.
In this case 66mm divided by 3,1416 = 21mm.
If measure in inches, for instance: 2.5 inches x 8.09 = 20.2mm