These are caps for volumetric flasks. The caps on these tend to get lost easily. Meant to keep dust out when stored, but if you get a tight enough fit can be used as a stopper, possibly in conjuction with some parafilm. The fusion360 file is parametric and most of the measurments are in reference to the “flaskouterlipdiameter,” so you will have to adjust that until you get a good fit. I included step files that fit my 250, 500, and 1000 mL volumetric flasks.
The author marked this model as their own original creation.