8 mm Test Tube Stoppers — LDPE, Green, Plug-In Friction Fit | 1000/Bag (300-2908-G20)
These green Low-Density Polyethylene (LDPE) stopper caps are designed to close 8 mm OD test tubes, culture tubes, and micro test tubes with a plug-in friction fit that seats against the inner tube wall without threading or snap-over engagement. Supplied non-sterile in convenient 1000/Bag bulk packaging, part number 300-2908-G20 is suited to high-volume tube capping programs in clinical, microbiology, and research laboratories. LDPE's inherent flexibility allows the stopper to compress on insertion and recover to maintain a positive, retained seal across a temperature range of −20 °C to +60 °C — covering frozen archiving through incubation conditions in a single closure format.
Technical Specifications
| Specification | Value |
|---|---|
| Part Number (MPN) | 300-2908-G20 |
| Tube OD | 8 mm |
| Cap Style | Stopper — plug-in friction fit |
| Material | Low-Density Polyethylene (LDPE) |
| Color | Green |
| Temperature Range | −20 °C to +60 °C |
| Sterility | Non-Sterile |
| Pack Size | 1000/Bag |
| BPA / Phthalates | BPA-free; no phthalate plasticizers |
| Country of Origin | USA |
Applications
- Microbiology culture tube capping: Seals TSB, BHI broth, and general culture tubes to prevent contamination during incubation while maintaining the friction-fit closure through repeated handling.
- Specimen tube archiving: Closes serum, plasma, and urine tubes during refrigerated storage (2–8 °C) and frozen archiving (−20 °C) without stopper hardening or loss of retention.
- Clinical chemistry pre-analytical hold: Prevents evaporation from open sample tubes during pre-analytical processing delays on the bench or in the analyzer rack.
- Pneumatic tube transport: Friction-fit plug closure retains tube contents during pressure changes encountered in hospital pneumatic transport systems.
- Color-coded tube routing: Green stoppers support laboratory color-coding protocols to visually differentiate specimen types, processing batches, or patient cohort groups at a glance.
Chemical Resistance
| Reagent / Condition | Compatibility |
|---|---|
| Aqueous buffers and saline | Excellent |
| Urine, serum, plasma matrices | Excellent |
| Dilute acids and bases | Good |
| Broth culture media (TSB, BHI) | Excellent |
| Alcohols (short-term contact) | Good |
| Chlorinated or aromatic solvents | Not recommended |
| Acetone / ketones | Not recommended |
Quality & Procurement
Made in USA, these Caplugs® Evergreen stoppers are manufactured from BPA-free, phthalate-free LDPE resin and shipped from domestic inventory by LabSupplies.com, an authorized dealer of the full Caplugs® Evergreen consumables line. The 1000/Bag pack size is sized for high-throughput tube capping programs, and tiered volume pricing is available for institutional, hospital, and grant-funded procurement accounts. Orders for stocking items typically ship same business day.
Frequently Asked Questions
What tube types fit these stoppers?
The 300-2908-G20 is designed for disposable glass and polystyrene culture tubes, micro test tubes, and general laboratory test tubes with an 8 mm outer diameter. Always verify tube OD against the stopper specification before placing high-volume orders.
Why is LDPE used instead of polypropylene or polystyrene for stopper-style closures?
LDPE's low-density flex modulus allows the stopper plug to compress under insertion force and then recover to grip the inner tube wall. Rigid materials such as PP, PS, and HDPE lack this compliance and would crack or fail to retain — making LDPE the appropriate material choice specifically for friction-fit stopper formats.
Will these stoppers stay sealed through freeze-thaw cycles?
Yes. LDPE maintains its flexibility down to −20 °C, so the stopper does not harden or lose friction-fit engagement during frozen archiving or through repeated freeze-thaw cycles, unlike stiffer thermoplastics that become brittle at low temperatures.
Are these stoppers sterile?
No — they are supplied non-sterile in 1000/Bag bulk packaging. For applications requiring sterile closures, contact LabSupplies.com to confirm current product availability in sterile formats within the Caplugs® Evergreen stopper line.