Magnetic Stirrer Bars

A magnetic stirrer bar, also called a stir bar, spin bar, or PTFE stir bar, is a small magnetised rod sealed in a chemically inert coating that spins inside a beaker or flask when placed on a magnetic stirrer. It is the essential consumable behind every magnetic mixing setup, available in a range of shapes and sizes to suit different vessels, volumes, and mixing needs.

SmartLabs stocks magnetic stirrer bars for general chemistry, biology, and industrial laboratory use across South Africa, from small bars for everyday beaker mixing to larger bars for flasks and bigger volumes. Built to resist common acids, solvents, and bases, these stir bars are designed for repeated use alongside any compatible magnetic stirrer, making them a reliable, low cost staple for any lab bench.

PTFE stir bar spinning inside a beaker on a magnetic stirrer

What is a magnetic stirrer bar?

A magnetic stirrer bar, also called a stir bar or flea, is a small rod of magnetised metal sealed inside a chemically inert PTFE coating. Dropped into a beaker or flask, it spins in place when placed on a magnetic stirrer, mixing the liquid without any external shaft or blade entering the container.

SmartLabs stocks stir bars in several shapes and sizes, plain cylindrical bars for general use, cross and star shapes for extra turbulence, and octagonal bars that sit more stably on a flat vessel base. The PTFE coating resists most acids, solvents, and bases, so the same bar can be reused across a wide range of chemistry work.

Common uses of magnetic stirrer bars in the lab

Different shapes and sizes suit different containers and mixing needs.

  • Dropping a cylindrical PTFE stir bar into an empty beaker

    General beaker mixing

    A plain cylindrical bar dropped into a beaker before adding liquid is the standard setup for routine mixing and dissolving on any magnetic stirrer.

  • Cross-shaped stir bar spinning in a round-bottom flask

    Extra turbulence in round-bottom flasks

    Cross and star-shaped bars create more turbulence and follow the curved base of a round-bottom flask more effectively than a plain cylinder.

  • Octagonal stir bar in a flask of viscous liquid

    Larger volumes and viscous liquids

    Larger, octagonal bars sit more stably on a flat vessel base, giving reliable spinning in bigger flasks or thicker liquids that would stall a small bar.

  • Comparing different sizes of magnetic stir bars

    Building a size range

    Most labs keep a small selection of bar sizes on hand, since the right bar length depends on the container and volume being mixed each time.

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