Sorry for the late response. The width of the opening is 2" and the height is 1-5/8" minimum to 1-3/4" max. There are ribs on the top surface that slide on the top of the tube and why I can't give you a more accurate measurement. I believe 1-3/4" would be a tight fit. Sorry I can't be more accurate. I no longer have the Thule rack and can't give you the exact measurement of the tube. These are for the Thule T2 rack. So if you are able to ask someone who has a T2 rack to measure the tube you would have a very accurate measurement.
Thanks kindly ..... Marco