These are inserts for the Spool Holders linked below that fit up to 6x V6-Style nozzles (M6x1).
As the hole goes deep enough it should be able to fit Volcano-style nozzles as well (please confirm!)
Why not use the space you already have? (In case you already printed a custom spoolholder, that is.)
https://www.printables.com/de/model/88353-spool-holder
The author remixed this model.