Stir bar with "pivot ring" in the center to reduce friction against the bottom of the flask, allowing it to spin faster and more easily.

Add to the flask when propagating yeast on a stir plate. Can be boiled in the flask along with starter wort. Always a good idea to have spares on hand in case you pour the stir bar into the fermenter along with the starter! 50 mm size is best for 2000 or 5000 ml flasks.