What are the 3 bumps/ridges on the green flex barium nozzles for?

I have been looking at the larger (usually green) "Barium type" or "plastisol" or "N-Tip" nozzles and wondering why they have the three ridges or bumps under the head. For play they definitely can add to the stimulation if it is wiggled or thrust in the anus, but I doubt that is the original purpose. It could be "measuring" to see how far inside the head is, but that doesn't make much sense. Does anyone know?

Picture of the nozzle here:

https://en.zity.biz/index.php?mx=gallizz;ox=imagedownload;image;img=287497