clamp size is determined by the outside diameter of the tube. Measure
the circumference of your tube where the clamp will mount, and divide
the diameter by 3.14 to determine the outside pipe diameter. For
example, if the tube measures 6 inches around, then 6 divided by 3.14
equals 1.91. Your tube outside diameter is 1.91" and that is the
correct clamp to choose.