These 1" x 5/16" magnetic stir bars come encapsulated in FDA approved PTFE with Alnico V magnet cores. They are nicely polished to reduce pick-up and cross contamination and can be sterilized using thermal or chemical means. To prevent demagnetization please do not store bundles of random stir bars together, do not drop on hard (especially steel) surfaces, and try to store in identical pairs. A couple of recommendations for choosing stir bars....stirring is most effective when the distance between the poles in the drive magnet (in the stirrer) is most similar to the length of the stir bar. Also, the closer the proximity of the drive magnet (in the stirrer) to the stir bar, the more advantageous. The pictured stir bar is exactly what you recieve. See specifactions below for more details. ALL OUR STIR BARS SHIP FOR FREE!