This hard-to-find stopper is now a Weber Scientific Exclusive. 75 mm long soft flexible rubber with a 42 mm long extension to keep stopper from falling out during autoclaving. As specified in APHA, Standard Methods for the Examination of Dairy Products, this is the stopper of choice for all plain neck dilution bottles, yet is suitable for use on screw finish bottles as well. High-quality rubber is repeatedly sterilizable.