These stir bars are magnetic, and coated in PTFE, no harm to human body, and heat resistant to 250 celsius degree The PTFE coatings are intended to be chemically inert, not contaminating or reacting with the reaction mixture they are in Elliptical (egg shaped) magnetic stirring bars are particularly well suitedfor round bottom flasks. Their shape mimics that of a flask and ensurescomplete mixing. They also offer minimal contact when used in plasticcontainers Magnetic stirrers can only be used for relatively small experiments of 4 liters or less.The mixing process is quieter and more efficient, and the stirrer is not exposed to the external transmission component so it is not easily damaged Stir bars help to build a relatively economical, environmentally friendly, and safe device that can greatly save manpower and reduce the use rate of flames, and relatively improve the safety of laboratories and home brewing Package Includes: 1 Piece stir bar