Step 1: Take an open-ended wrench and slide it into the bar/tubing
Step 2: Make sure wrench fits snug around rack bar/tubing
Step 3: Reference wrench size to the sizes down below. (Most likely will be 1/2 or 5/8)

The String Method is great for anyone with a round luggage rack and who does not have a caliper/micrometer and will provide a fairly accurate measurement to see which mounting bracket you should choose. You will need a piece of string or a thin piece of paper that can wrap around the tubing and also a marker.

Step 1: Grab a piece of string that is at least 3 inches in length (easier to handle)
Step 2: Wrap the piece of string around your luggage rack tubing in your desired spot you would like to mount your flag mount. Make sure to have string taught and make sure to overlap string
Step 3: Take marker and mark over top of both parts of the string. Make it dark enough that you will be able to measure off of.
Step 4: Take a ruler and measure the distance between both marks on the string.
Step 5: Once you have this measurement reference the number in inches to the chart below as to what mounting bracket you should choose.
Step 6: Measure the width of the area you are wanting to put your flag mount and make sure there is at least 1.25″ of clearance that the mounting bracket can fit between. Be sure to take into consideration the welds if mounting between bars.

The Tape Measure method is perfect for anyone who has a square rack but is slightly less recommended for anyone with a round rack.

Step 1: Grab your tape measure
Step 2: Pull the tape out and hold up on top of the tubing where you would desire to have your flag mount mounted.
Step 3: Take a measurement of the width of the tubing (make sure your eyes are directly above the tape measure looking straight down)
Step 4: Take a measurement of the width of where you plan on mounting the bracket.  Make sure there is at least 1.25″ of clearance. Take into consideration the welds if mounting between bars.