MEDIUM Universal Solid P.E.T. Bung (Stopper) Size #10 - Fits ALL of our P.E.T. carboys. Replaces a number 10 rubber bung and a much better fit! White bung with a longer taper for a snugger fit and better seal. 100 per cent FDA approved material and NO BPA! Lip prevents bung from falling into carboy. Will not dry out like natural rubber stoppers!