Caplugs® Evergreen
Test Tube Stoppers, HDPE, Natural — 300-4708-020 | 1000/Bag | Caplugs® Evergreen
Test Tube Stoppers, HDPE, Natural — 300-4708-020 | 1000/Bag | Caplugs® Evergreen
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Flat Top Test Tube Stopper Caps, For 8 mm Test Tubes, LDPE, Natural — 300-4708-020 | 1000/Bag
| Quick Reference — 300-4708-020 | |
|---|---|
| Tube OD | 8 mm |
| Cap Type | Flat-top stopper (plug-in friction fit) |
| Profile | Flat top — flush with tube rim when seated |
| Material | Low-Density Polyethylene (LDPE) |
| Color | Natural |
| vs Standard | Flat top sits flush; standard stopper has dome profile |
| Temp Range | -20°C to +60°C (LDPE flex range) |
| Sterility | Non-Sterile |
| Pack Size | 1000 / Bag |
| Price | $57.85 / Bag ($0.0579 / stopper) |
Technical Narrative
The Caplugs® Evergreen is a natural LDPE flat-top stopper cap for 8 mm OD test tubes — the flat-profile variant of the friction-fit stopper cap design. The flat-top profile positions the cap top surface flush with the tube rim when fully seated, rather than projecting above it as a standard dome stopper would. This flush profile provides two advantages: (1) improved stacking in test tube racks — flat-top stoppers allow tubes to be stacked or inverted without the cap profile preventing full seating in rack positions; (2) reduced cap protrusion in automated tube handling systems and tube readers where a projecting dome cap can interfere with instrument clearance.
LDPE construction provides the flex required for friction-fit stopper retention across repeated insertion/removal cycles — the same material rationale as the 300-29xx series standard dome stoppers. LDPE retains flexibility from -20°C through 60°C and is chemically inert to serum, plasma, and standard aqueous specimen matrices. At $57.85 per 1000/Bag — $0.0579 per stopper — the flat-top format delivers per-unit economics for high-volume 8 mm tube programs.
Technical Specifications — Caplugs® Evergreen
| Specification | Value |
|---|---|
| Part Number | |
| Caplugs Item # | 3004708020E1 |
| Tube OD | 8 mm |
| Cap Style | Flat-top stopper — plug-in friction fit |
| Profile | Flat top — cap top flush with tube rim when fully seated |
| Material | Low-Density Polyethylene (LDPE) |
| Color | Natural |
| Tube Types | 8 mm OD glass and PP/PS test tubes |
| Temp Range | -20°C to +60°C |
| Sterility | Non-Sterile |
| Pack Size | 1000 / Bag |
| BPA/Phthalate | BPA-free; no phthalate plasticizers |
| Country of Origin | Made in U.S.A. (California) |
Flat Top Stopper Application Compatibility — 8 mm Tubes
The LDPE flat-top stopper fits 8 mm OD test tubes for:
| Application | Tube / Specimen | Notes |
|---|---|---|
| 8 mm test tube capping | 8 mm OD glass and plastic test tubes | Flat-top LDPE stopper — friction fit into tube opening |
| Culture tube closure | Microbiology broth culture in 8 mm tubes | Flat top profile vs standard dome stopper |
| Specimen tube archiving | Serum, plasma in refrigerated/frozen storage | LDPE stopper seals tube during cold storage |
| Color routing (natural) | Universal cap for any labeling system | Natural LDPE for secondary label identification |
| Reagent / stock tube | Buffer, enzyme, reagent aliquots in 8 mm | Flat-top stopper as reusable tube closure |
| Clinical chemistry tubes | Pre-analysis 8 mm sample tube closure | Flat profile flush with tube rim for rack stacking |
| Hematology tubes | 8 mm EDTA and anticoagulant tube formats | LDPE inert to anticoagulant specimens |
| Replacement caps | Replacement for lost/damaged tube closures | 1000/Bag bulk format for high-volume programs |
Validate stopper fit with your tube brand before bulk purchase. Request a free sample to confirm friction-fit retention.
Chemical Resistance — Low-Density Polyethylene (LDPE)
LDPE provides flexibility for stopper friction-fit retention and inertness to clinical specimen matrices.
| Reagent / Condition | Compatibility |
|---|---|
| Aqueous buffers / water | ✓ Excellent |
| Urine / serum / plasma | ✓ Excellent |
| Dilute acids (<10%) | ✓ Good |
| Short-chain alcohols | ✓ Good |
| DMSO (≤10%) | ✓ Good — brief contact |
| Autoclave (121°C) | ✗ Not compatible — LDPE softens |
| Storage at -20°C | ✓ Suitable — LDPE retains flexibility |
Laboratory Applications
The serves clinical chemistry and hematology laboratories using 8 mm test tubes in automated tube readers or stacking rack formats where flat-profile stoppers reduce clearance conflicts; microbiology programs capping 8 mm culture tubes for incubation; and any 8 mm test tube workflow where the flat-top stopper profile is preferred over the standard dome.
U.S. Manufacturing, Quality & Institutional Procurement
Every Caplugs® Evergreen lot is precision-molded at our California manufacturing facility. We supply reference laboratories, hospital systems, and federal procurement offices under institutional pricing programs. Request a free sample below to validate fit before committing to volume.
Frequently Asked Questions — Caplugs® Evergreen
What is the difference between a flat-top stopper and a standard dome stopper for 8 mm tubes?
The flat-top stopper has a flat top surface that sits flush with the tube rim when fully seated. Standard dome stoppers (e.g., 300-2908 series) have a convex dome that projects above the tube rim. The flat top is preferred in rack-stacking programs where dome projections interfere with full seating, and in automated tube handling where instrument clearance is tight. Both are LDPE friction-fit stoppers with identical tube compatibility for 8 mm OD tubes.
Is the flat-top stopper compatible with the same 8 mm tubes as the dome stoppers?
Yes. The fits the same 8 mm OD test tube formats as the standard dome stoppers (300-2908-020 natural, 300-2908-G20 green). All 8 mm stoppers in the Caplugs® Evergreen range are LDPE friction-fit for 8 mm OD glass and PP/PS test tubes. The only functional difference between flat-top and dome-top is the cap profile above the tube rim. Validate fit with a sample before bulk purchase.
Why is LDPE used for stopper caps rather than PP or HDPE?
LDPE's low-density flex modulus provides the compression and spring-back required for friction-fit stopper retention across repeated insertion/removal cycles. PP and HDPE are too rigid for stopper-style plug-in engagement — they crack under repeated insertion/removal rather than flexing. LDPE also retains flexibility at -20°C to prevent brittle fracture during frozen stopper removal. For screw-thread tube caps (300-3010/300-3532/300-3541), HDPE is the correct material — but for friction-fit stoppers, LDPE is the only appropriate specification.
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