15–21 mL Test Tubes, Screw Caps, PS, Red — 214-2099-R50 | 1000/Bag | Caplugs® Evergreen

21 mL Round-Bottom Test Tubes with Red Screw Caps — PS, Natural, 16 × 150 mm (214-2099-R50)

These 21 mL polystyrene round-bottom test tubes are the largest round-bottom option in the Caplugs® Evergreen catalog, measuring 16 × 150 mm and supplied with red screw caps — packaged 1000/Bag unassembled so tubes and caps ship separately for assembly at the point of use. The generous working volume supports bulk reagent preparation, large-volume culture and reaction workflows, and extended inversion mixing, while the resealable red screw cap allows re-closing for sample storage, transport, and reflex testing without aliquot transfer. Supplied non-sterile, these tubes are ready for high-throughput clinical and research workflows where color-coded rack management and maximum tube length are priorities.

Technical Specifications

Applications

• Sample storage at refrigerated (4 °C) or frozen (−20 °C) conditions — the red cap provides immediate visual cohort identification at rack level
• Sample transport in tube carriers or secondary containment bags where a leak-resistant screw-cap closure is required
• Reflex and add-on testing — re-cap and refrigerate after an initial analytical run without transferring to a secondary tube
• Bulk reagent, calibrator, and buffer preparation requiring multi-day sealed storage at 21 mL working volume
• Water bath incubation at 37 °C in standard 16 mm tube racks
• Manual inversion mixing protocols benefiting from the maximum headspace provided by the longest tube in this family
• Clinical centrifugation in 16 mm rotor configurations
• Color-coded rack management — red cap convention aligns with STAT sample escalation, critical-value flagging, infectious disease panel segregation, and red-top collection tube workflows

Chemical Resistance

Quality & Procurement

Made in USA, these Caplugs® Evergreen tubes are manufactured from FDA-compliant, BPA-free, phthalate-free, latex-free polystyrene resin under ISO 9001 quality management controls. The natural PS tube wall provides optical clarity suitable for direct visual inspection and spectrophotometric reading of tube contents. The unassembled pack format — tubes and caps supplied separately — lets laboratory staff apply caps at the point of sealing, minimizing open-tube exposure time in high-throughput workflows and simplifying bulk dispensing. LabSupplies.com is an authorized dealer of Caplugs® Evergreen consumables and ships from USA inventory, typically same business day for stocking items, with volume pricing available for institutional and grant-funded laboratories ordering at scale.

Frequently Asked Questions

Are these tubes sterile?
No — these tubes are supplied non-sterile and are intended for clinical chemistry, reagent preparation, sample storage, and other applications that do not require a sterile article. If sterility is required for your workflow, consult your laboratory's validation protocols for an appropriate decontamination step.

Why are the tubes and caps shipped unassembled?
The unassembled pack format allows staff to apply caps at the moment of sealing rather than storing pre-capped tubes. This reduces the open-tube exposure window in high-throughput settings and gives labs flexibility in applying caps only to tubes that are actively in use.

Can these tubes be used with a centrifuge?
Yes — the 16 × 150 mm round-bottom geometry is compatible with clinical centrifuge rotors designed for 16 mm tubes. Always verify your centrifuge rotor specifications and maximum rated speed for this tube format before use.

Are other cap colors available in this same tube format?
Yes — the 21 mL 16 × 150 mm PS round-bottom tube is available with blue, orange, green, lavender, red, and yellow screw caps, enabling a complete color-coded rack management system across sample classes or test panels. A tubes-only (no cap) option is also available for labs that source caps separately.