Standard octagonal stir bars are designed for flat-bottom vessels — but many laboratory flasks, round-bottom flasks, and specialty glassware have concave or curved bottoms where an octagonal bar rattles, wobbles, and loses magnetic contact at higher speeds. The Heathrow Scientific PTFE Smooth Magnetic Stir Bar series is specifically designed for concave-bottom glassware: the smooth cylindrical profile maintains continuous contact with curved vessel floors, providing more stable coupling and quieter operation in the round-bottom and concave-bottom containers common in chemistry and biochemistry labs.
Like the Octagonal series, these bars use an Alnico magnet core encapsulated in chemical-resistant PTFE, withstand temperatures up to 250°C, and are autoclavable for sterile applications. Available in four sizes from 10×5mm through 35×8mm, sold in packs of 10.
Features and Benefits
Smooth Profile Optimized for Concave-Bottom Glassware: The cylindrical smooth surface conforms better to the curved interior of round-bottom flasks, Erlenmeyer flasks with concave bases, and specialty vessels — maintaining continuous floor contact for stable, chatter-free rotation at high speeds.
Alnico Magnet Core — Strong Permanent Coupling: Alnico magnet material provides superior coupling strength compared to ferrite alternatives — maintaining rotation lock in larger vessels and at higher speeds where weaker magnets decouple and spin out.
PTFE Encapsulation — Inert, Chemical-Resistant Coating: Full PTFE coating is inert to virtually all laboratory chemicals including strong acids, bases, and organic solvents — protecting the magnet core and preventing ionic contamination of the stirred solution across the pH and chemical spectrum.
250°C Maximum Temperature — Heated Stirring Compatible: PTFE stability to 250°C makes these bars safe for use on hot plate stirrers during heated mixing applications including titrations, reflux, dissolution testing, and thermally controlled reactions.
Autoclavable for Sterile Applications: Withstands standard autoclave cycles for use in sterile cell culture, media preparation, and pharmaceutical manufacturing environments where contamination-free mixing conditions are required.
Four Sizes, Pack of 10 — Versatile Coverage: The 10×5mm through 35×8mm range covers small vials and test tubes up to large 3L vessels — and the pack of 10 provides immediate replacement stock for labs that go through stir bars regularly.
Specifications
| Property | Value |
|---|---|
| SKU Series | 120894 (10×5mm), 120895 (25×8mm), 120896 (30×8mm), 120897 (35×8mm) |
| Brand | Heathrow Scientific |
| Material | PTFE encapsulation / Alnico magnet core |
| Shape | Smooth cylindrical (optimized for concave-bottom vessels) |
| Color | White |
| Pack Size | Pack of 10 |
| Max Temperature | 250°C |
| Autoclavable | Yes |
| Country of Origin | China |
Laboratory Applications
Round-Bottom Flask Stirring in Chemistry: Use in round-bottom flasks for organic synthesis, reflux reactions, and distillation setups where the smooth profile maintains reliable floor contact in the curved vessel bottom — eliminating the wobble that octagonal bars produce in round-bottom geometry.
Erlenmeyer Flask & Conical Vessel Mixing: The smooth profile is well-suited to the slightly concave bottom geometry of Erlenmeyer flasks used in titrations, culture media preparation, and standard chemistry protocols.
Pharmaceutical & Biochemistry Research: Mix enzyme reactions, protein solutions, and pharmaceutical formulations in concave-bottom reaction vessels where a stable, low-vibration stir bar is required to prevent foam formation and protect shear-sensitive samples.
Heated Reaction Mixtures: The 250°C temperature tolerance makes these bars the correct choice for hot plate-stirred reactions including recrystallizations, titrations, dissolution testing, and synthesis protocols requiring simultaneous heat and agitation.
Frequently Asked Questions
When should I use Smooth stir bars instead of Octagonal Pivot Ring bars?
Use Smooth bars (120894–120897) in round-bottom flasks, Erlenmeyer flasks, and any vessel with a concave or curved bottom — the smooth profile maintains consistent floor contact in curved geometries. Use Octagonal Pivot Ring bars (120547–120552) in flat-bottom beakers, crystallizing dishes, and vessels with flat floors where the pivot ring and octagonal turbulence characteristics are most effective.
What size smooth stir bar should I use for my flask?
For flasks under 250mL, use 10–25mm bars. For 250–500mL flasks, use 25–30mm bars. For 500mL–2L flasks, use 30–35mm bars. As a general guideline, choose a bar that is approximately 1/3 to 1/2 the vessel's internal diameter at the bottom.
Are the Smooth bars compatible with the Heathrow Scientific Magnetic Induction Stirrer?
Yes. All Alnico-core PTFE stir bars are compatible with the Heathrow Scientific Magnetic Induction Stirrer (120584/120585) and all standard motor-driven magnetic stirrer platforms.
Quality Assurance
Heathrow Scientific PTFE stir bars are manufactured with sintered Alnico cores and full PTFE encapsulation under rigorous quality standards. Each production lot is inspected for coating uniformity and dimensional accuracy to ensure reliable, contamination-free performance in concave-bottom laboratory glassware.
Academic and Institutional Pricing
LabSupplies.com offers tiered quantity pricing for academic and research institutions. As an authorized dealer, we ship directly from USA inventory.