Grüezi Pallas and welcome to this forum
I think you assumption is right. They look very much as a tripod part. These sleeves are used in the tripod tubes to keep them looked once they extended and locked. Yours look like they are made of some kind of glass fibre material...
I checked my old generation ALFAE tripod and it have very similar sleeves as yours. See the attached photos
Are they from FOBA?
I don't really know... How conclude you that they are from FOBA? Any indications?
Some FOBA tripods use parts that look as they are made by Gitzo... I am pretty sure Gitzo rebranded stuff for FOBA...
Would I keep it?
Definitely or sell it on the usual market places! Spare parts are always welcome! I regret all the stuff I couldn't save during the FOBA closure...
Hope that helps
View attachment 4890010
here the tripod in question, a old gen of ALFAE where the center column is screwed with three screws
View attachment 4890011