This pack of 10 polypropylene stoppers is designed to fit 19/26 sockets. The stoppers are lightweight, durable, acid-proof, and autoclavable, making them a practical choice for a variety of laboratory glassware applications. The polypropylene construction provides chemical resistance and withstands repeated sterilization cycles. These stoppers offer a reliable seal for flasks, cylinders, and other labware with standard 19/26 joints.