RS-9-2 Rubber Stoppers, Size 9, Drilled 2-Holes (1-Pound Pack),Black

The stopper is hard and does not fit properly on the conical flask. My son could not record the right data for temperature-volume graph and Pressure-volume graph. The poor boy was unable present good enough science project for thermal expansion of water. I odered twice to be sure of the standard. Terms and conditions for odering not favorable

This RS-9-2 Size fits the Five Gallon Glass Carboys, I use them on my first jug on my RO/DI Cascade system for the Ultra Pure water. See my comment on the RS-10-2 size plugs.