12 mm Test Tube Stoppers — Blue LDPE Plug-In Friction-Fit Caps for 12 × 75 mm Tubes (300-2912-B20)
These blue low-density polyethylene stopper caps provide a secure plug-in friction-fit closure for 12 mm OD test tubes — one of the most widely used diameters in clinical chemistry, hematology, microbiology, and research workflows. Supplied non-sterile in economical 1000/Bag packaging, part number 300-2912-B20 maintains reliable stopper retention across a working temperature range of −20 °C to +60 °C, making these caps equally suited to frozen archive storage and routine incubation. The blue color mirrors the CLSI H3 convention for citrate anticoagulant tubes, supporting color-coded specimen routing and batch identification without additional labeling.
Technical Specifications
| Specification | Value |
|---|---|
| Part Number (MPN) | 300-2912-B20 |
| Tube OD | 12 mm |
| Compatible Tube Format | Standard 12 × 75 mm test tubes |
| Cap Style | Stopper — plug-in friction fit |
| Material | Low-Density Polyethylene (LDPE) |
| Color | Blue |
| 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
- Specimen tube archiving: Prevents evaporation and contamination during refrigerated or frozen storage of serum, plasma, and urine samples through full freeze-thaw cycles
- Clinical chemistry: Seals sample tubes prior to analysis; LDPE is inert to serum and plasma matrices, ensuring no leaching into specimen contents
- Microbiology culture tubes: Retains friction-fit seal on TSB, BHI, LB broth, and other culture media tubes throughout 37 °C incubation
- Cell culture: Caps suspension cell culture and virus propagation tubes while allowing practical handling between incubation steps
- Pneumatic tube transport: LDPE flex retention withstands the acceleration forces of clinical pneumatic tube transport systems without loosening
- Color-coded batch routing: Blue stoppers visually distinguish citrate-anticoagulated specimens or priority batches in loading racks, consistent with CLSI H3 color conventions
Chemical Resistance
| Reagent / Condition | Compatibility |
|---|---|
| Aqueous buffers / saline | Excellent |
| Serum, plasma, urine | Excellent |
| Broth media (TSB, BHI, LB) | Excellent |
| Dilute acids and bases | Good |
| Alcohols (short-term contact) | Good |
| Chlorinated / aromatic solvents | Not recommended |
| Autoclaving | Not recommended |
Quality & Procurement
Made in USA, these Caplugs® Evergreen stopper caps are manufactured from BPA-free, phthalate-free LDPE resin. LDPE's inherent flex modulus allows the stopper plug to compress on insertion and spring back against the tube inner wall, maintaining positive friction-fit engagement through repeated insertion and removal cycles — from −20 °C frozen archive through 60 °C incubation — without hardening or losing closure integrity. LabSupplies.com is an authorized dealer of Caplugs® Evergreen consumables and ships from USA inventory, with tiered volume pricing available for high-throughput clinical laboratories, research institutions, and procurement programs purchasing across multiple color variants.
Frequently Asked Questions
Will these stoppers fit BD® Vacutainer® and other standard 12 × 75 mm tubes?
These caps are designed for 12 mm OD test tubes in the standard 12 × 75 mm format common across clinical and research tube brands. Always verify your specific tube's outer diameter before switching from OEM closures, as wall thickness can vary slightly between manufacturers.
Are these stoppers sterile?
No — they are supplied non-sterile in 1000/Bag packaging. For workflows requiring sterile closures, treat or select an appropriate sterile-packaged alternative.
Can these be used for frozen specimen storage?
Yes. The LDPE material remains flexible down to −20 °C, so the friction-fit seal is maintained through freeze-thaw cycles without the stopper hardening or losing engagement with the tube wall.
Why blue? Does the color carry a specific meaning in the lab?
Blue aligns with the CLSI H3 convention for citrate anticoagulant collection tubes, making these stoppers a natural choice for re-capping blue-top specimens after collection and for visually differentiating citrate batches in color-coded specimen routing systems. The color is inherent to the LDPE resin and does not affect chemical compatibility.