LAB - Magnetic Stir Bars Guide

Magnetic spin bars are useful for laboratory stirring and allow for precise mixing without mechanical parts touching the fluid, unattended operation and prevent contamination. They are ideal for small-scale, low-viscosity applications where consistency and cleanliness are critical, offering better control than manual stirring.

Benefits:

• Contamination-free – Bars are coated with PTFE or glass, so no lubricants or metal parts enter the liquid, crucial for sensitive experiments.
• Quiet and efficient – Magnetic spin bars create vortexes and uniform movement compared to manual stirring
• Automation, precision and consistency – The motorised stirring base can stir consistenenty for long periods and also keep solutions at constant temperatures
• Easy to clean and handle – Simple bar designs make them easy to sterilise with magnetised coated retrieval tools to remove the bar from the solution.

Things to consider when choosing a stirring bar for your application:

Size – The bar needs to be able to fit through the opening of the vessel being used.

Shape – Each bar shape has a slightly different effect. See the table below to choose from the range of shape options to consider,

Composition – Magnetic stirring bars coated with PTFE (Teflon) are heat resistant and chemically inert, but glass coated options are ideal for very high temperature applications, as well as for use with abrasive materials.

Rare Earth stirring bars – Identified by a carbon black spot on the bar, they have a much greater magnetic strength, making them useful for stirring viscous samples and are almost completely resistant to demagnetisation, so don’t require regular replacement.

It can also be useful to consider mechanical (overhead) stirring. Sometimes magnetic stirring may not be sufficient if your sample is particularly viscous, or the viscosity is expected to increase during the experiment, magnetic stirring will likely not be powerful enough for the mixing process. Similarly, if there are solids or crystals in your sample then the magnetic stirring bar may grind them between the stirrer and the glass. In these instances, the use of an overhead stirrer is advised, there are also various stirring shafts available.

Magnetic Spin Bar Shapes

Stir Bar	Stirring Style	Vessel Type
	Cross Good general-purpose bars that create deep vortices and strong turbulence. The cross shape excels at stirring sediments, dissolving solids and provides stable, quiet operation. Their design helps prevent "jumping" and ensures consistent results.	Beakers and flasks
	Crosshead Crosshead stir bars create strong, turbulent mixing at low speeds, preventing splashing and sedimentation by engaging the top, bottom, and sides of the vessel.	Narrow test tubes, cuvettes, and flasks
	Cylindrical (Plain) Excellent general-purpose bars that offer smooth, consistent, and quiet mixing for routine tasks like dissolving solids, preparing solutions and maintaining uniform liquid phases.	Beakers, flasks and flat-bottomed labware
	Disc Disc stir bars (often cross-shaped or with angled vanes) create strong turbulence and efficient mixing by generating powerful vortexes without requiring a hole in the container. Ideal for general lab applications like preparing solutions, titrations, and growing cultures.	Deep vessels
	Double-ended Excellent for creating strong turbulence and efficient mixing, offering better centering and less contact surface than traditional bars. Ideal for low speeds, uniform mixing in sealed systems,breaking up sediment, dissolving solids, and preventing buildup on vessel walls and are great for creating suspensions.	Tall or narrow vessels like test tubes or cylinders
	Flute Flute (or bone/cross/triangle) stir bars create strong turbulence at lower speeds, preventing splashing, and handling viscous fluids or solids that need scraping/suspension. Ideal for yeast starters, chemical reactions, and dissolving powders.	Conical flasks or round-bottomed vessels
	Hub Hub stir bars, often with a central pivot ring for stability, are excellent for general lab mixing at slow speeds. Ideal for titrations, sample preperation, cell cultures, and chemical reactions. Their design (like the pivot ring) helps them stay centered and mix efficiently in curved containers	Round or uneven-bottomed flasks
	Micro (Flea) Designed for stirring small volumes particularly useful for environmental testing and life science applications in which small sample volumes need to be prepared and evaluated.	Vials, tubes, gradient makers spectrophotometer cells
	Octahedral Designed to create more turbulence at low speeds while their angled surfaces and often integrated pivot rings reduce friction and help them adapt to different container shapes for smoother, more efficient mixing of low-to-medium viscosity fluids.	Vessels with uneven or curved bottoms, round-bottom flasks, vials, and tubes
	Oval Excellent for efficient, homogeneous mixing where standard bars might struggle, the shape conforms to curved surfaces for better contact and vortex formation. Often used in general lab work, chemistry, and life sciences.	Round-bottom flasks, vials, and curved vessels,
	Pivot Ring Provide a stable pivot for smoother, quieter mixing, reducing friction, and preventing the bar from "walking" to the side. Ideal for general chemistry, food preperation and reactions needing consistent, low-friction stirring in non-flat containers.	Flasks or vessels with curved/uneven bottoms
	Spherical Provide efficient, eccentric mixing due to centrifugal force pushing them to the wall, and are also used in bead mills or for creating microcapsules, ensuring thorough agitation in narrow spaces where other shapes might snag.	Small volume containers, test tubes and vials
	Square Create strong vortex action and intense turbulence, making them ideal for thoroughly mixing solutions, especially for suspensions. They prevent solids from settling by scraping the bottom, offering better efficiency than simple round bars for tough mixing jobs. They're used in labs for chemistry, biology, homebrewing, and even specialised uses like creating microcapsules	Larger vessels
	Tapered Great for stirring viscous liquids and for general use to create strong turbulence, center themselves well (especially octagonal ones), and move efficiently with less contact in plasticware. Ideal for strong mixing in tough-to-stir solutions like slurries or dissolving salts.	Small volumes in test tubes/narrow vessels and containers with sloped bottoms
	Triangular Excellent for dissolving solids, mixing sediments, and preventing residue buildup. Angled shape creates strong scraping action and high turbulence at lower speeds, ensuring thorough mixing and cleaning the container bottom effectively.	Large vessels
	Tube Provides rapid vertical and horizontal mixing with a minimum of vortexing when placed on a magnetic stirring machine. Centrifugal pumping action, generated by the cross channels in the upper face, mixes without aeration.	Spectrophotometer cells, cuvettes or test tubes
	Wing Great for general lab mixing in small to medium volumes (≤4L), offering quiet, spill-free stirring without external moving parts. Ideal for chemistry/biology research, yeast starters, and applications needing chemical resistance or gentle mixing.	Test tubes or flasks
	Glass Excellent for high-purity work, high-temperature applications, and with corrosive chemicals. Their borosilicate glass coating resists heat (up to 250°C+) and harsh substances, making them ideal for trace analysis and processes needing a clean, non-reactive stirrer.	Beakers, flasks and flat-bottomed labware

There are a range of Magnetic Retrival Tools available at ProSciTech.