For Bobbin Lace to prevent threads from rubbing against pins and pin holes while working.
If you prefer to buy one - see vansciverbobbinlace.com/tools.html

Used PRUSAslicer in 2 steps. I have included the 2 project files and the STL for both steps.
You want to use the final step to print.
Step 1
Add cylinder, add negative cylinder offset
Step 2
Add rounded corners(cylinders) and pin holes (negative cylinders)