These stir bars have a pivot ring around the center. They are designed to maintain the position in vessels with curved or uneven bottoms. The ring helps to reduce vibrations and wear, and reduce the effects of friction from contact with the . Mixer stir bar is made of PTFE. Not easy to demagnetize, will work longer than others. The laboratory bar is chemical resistant and corrosion resistant; The maximum temperature is 250 degrees centigrade and the minimum temperature is -196 degrees centigrade. Stirrer bar is widely applied in scientific research, universities, laboratories in the industrial and agricultural sectors as well as family usage. Specification: size:7 x 20mm Colour:White Material:PTFE Package Contents: 10 * rod magnetic mixer Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.