8 mm Test Tube Stoppers — Flat-Top HDPE Plug-in Friction Fit, Natural, 1000/Bag (300-4708-020)
These natural LDPE flat-top stopper caps are designed to friction-fit 8 mm OD glass and plastic test tubes, providing a flush, low-profile closure that sits level with the tube rim when fully seated. Supplied non-sterile in 1000/Bag bulk packaging, part number 300-4708-020 is an economical choice for high-volume clinical, hematology, and research tube programs that require a clean, rack-stackable cap. The flexible low-density polyethylene construction delivers the elasticity needed for secure plug-in retention through repeated insertion and removal cycles across a temperature range of −20°C to +60°C.
Technical Specifications
| Specification | Value |
|---|---|
| Part Number (MPN) | 300-4708-020 |
| Tube OD | 8 mm |
| Cap Style | Flat-top stopper — plug-in friction fit |
| Profile | Flat top — cap surface flush with tube rim when fully seated |
| Material | Low-Density Polyethylene (LDPE) |
| Color | Natural |
| Compatible Tube Types | 8 mm OD glass and PP/PS test tubes |
| 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
- Clinical chemistry and hematology: capping 8 mm sample tubes (serum, plasma, EDTA, anticoagulant) prior to analysis or archival storage
- Refrigerated and frozen specimen storage: LDPE remains flexible and retains its seal down to −20°C, keeping tubes securely closed through cold-chain handling
- Microbiology culture tube closure: flat-top profile accommodates incubator rack stacking without cap-to-cap interference
- Reagent and buffer aliquots: reusable friction-fit closure for enzyme stocks, buffers, and chemical reagents in 8 mm format tubes
- High-throughput tube programs: 1000/Bag bulk format supports replacement of lost or damaged closures across large tube inventories
- Automated tube handling: flush profile reduces cap protrusion that can interfere with instrument clearance in tube readers and automated rack systems
Chemical Resistance
| Reagent / Condition | Compatibility |
|---|---|
| Aqueous buffers / saline | Excellent |
| Serum and plasma matrices | Excellent |
| Dilute acids and bases | Good |
| Anticoagulant solutions (EDTA, heparin) | Excellent |
| Alcohols (ethanol, isopropanol) | Good — short-term contact |
| Acetone / chlorinated solvents | Not recommended |
| Aromatic solvents (toluene, xylene) | Not recommended |
Quality & Procurement
Made in USA, these Caplugs® Evergreen stoppers are manufactured from BPA-free, phthalate-free low-density polyethylene resin. LabSupplies.com is an authorized dealer of Caplugs® Evergreen laboratory consumables and ships from USA inventory, with tiered pricing available for high-volume institutional, clinical, and grant-funded purchasing programs. Customers evaluating a switch from their current tube closure supplier are encouraged to request a sample to confirm friction-fit retention with their specific tube brand before committing to bulk quantities.
Frequently Asked Questions
What is the difference between a flat-top stopper and a standard dome stopper?
A flat-top stopper sits flush with the tube rim when fully seated, while a standard dome stopper projects above the rim. The flush profile allows capped tubes to stack in rack positions without cap-height interference and reduces clearance issues in automated tube readers or handling systems.
Will these stoppers fit both glass and plastic test tubes?
Yes — the flat-top friction-fit design is compatible with 8 mm OD glass as well as polypropylene (PP) and polystyrene (PS) test tubes. Because wall thickness varies between tube brands and manufacturers, it is good practice to verify fit with a sample before purchasing in bulk.
Can these stoppers be used for frozen specimen storage?
The LDPE material retains its flexibility down to −20°C, so the stopper remains pliable and maintains a friction-fit seal during refrigerated and frozen storage. They are not intended for use below −20°C or in liquid nitrogen applications.
Are these stoppers sterile, and can they be autoclaved?
These caps are supplied non-sterile and are not designed for autoclave sterilization. LDPE has a service ceiling of +60°C, which is below standard autoclave temperatures. For sterile tube closure applications, a separately purchased sterile-packaged option would be required.