Boris
Old fat tired rider
Seems there are two variations on the shoulder of these racks. The shoulder for the loop frames are wider than the ones made for the ribbed tank style models. I did a comparison on this subject ages ago. Thought it might still be helpful. Perhaps a bit late for some? Hopefully not.
thecabe.com

Colson Stamped Racks | General Discussion About Old Bicycles
Does anyone know for certain if there were two separate pressings of different sizes for these Colson stamped racks? The collar on the left fits loopframes only, and the collar on the right fits the straight down tube rainbow frames only. Could the collar on the straight down tube rainbow rack...
