The Headband Flexbar with a solid circle has a higher clamping force. That means that it will feel tighter on your head.
The Headband Flexbar with a hollow circle has a lower clamping force. That means that it will feel looser on your head.
I just went through the build process and noticed that the symbols on the flexbars that I received were different than stated in the wiki section:
The tighter flexbar was a hollow circle with a square
The looser flexbar was a hollow circle with a circle.
It took me a while to figure out which flexbar was which, so it would be good to update that section with the right symbols.
This part of the wiki lists the headband flexbars as two types distinguished by:
I just went through the build process and noticed that the symbols on the flexbars that I received were different than stated in the wiki section: The tighter flexbar was a hollow circle with a square The looser flexbar was a hollow circle with a circle.
It took me a while to figure out which flexbar was which, so it would be good to update that section with the right symbols.