Hmmm.
I have dowel centering tooling for aligning hole centers for drilling. These are the type where you have the pilot marked or drilled one side then the discs center and mark the other board when clamped together.
Original items look like they’re meant to press fit and stay so, I don’t see them being used for patterning. Do look like they’re probably for table leaves though I’ve only ever seen wood dowels on leaves. Guess bougie tables might have used brass.