Laboratory Stoppers and Corks Singapore
A stopper is the smallest piece of glassware that decides whether an experiment stays contained. Flasks that must hold a vacuum, reagent bottles that travel between benches, shake flasks that vent gases and volumetric standards that must not evaporate all depend on a stopper that fits the joint exactly and tolerates the chemistry inside.
At JW RESEARCH SUPPLY, we supply laboratory stoppers and corks in ground glass, PTFE, silicone, natural rubber and nitrile to laboratories across Singapore, from school teaching labs to pharmaceutical QC and research institutes. This guide compares materials, joint standards and temperature limits so you select the right stopper for every vessel.
Stopper Material Comparison
| Material | Temperature Range | Chemical Resistance | Typical Use |
|---|---|---|---|
| Ground glass | Up to ≈ 400 °C | Excellent, except strong alkali | Volumetric flasks, reagent bottles |
| PTFE | -200 to 250 °C | Near universal | Solvent bottles, corrosive reagents |
| Silicone | -60 to 200 °C | Good, inert | Autoclaves, hot-water baths, shake flasks |
| Natural / nitrile rubber | -20 to 120 °C | Fair, swells with solvents | General bungs, tubing ports |
| Cork | Up to ≈ 120 °C | Poor with solvents | Storage bottles, teaching labs |
Common Joint and Bung Sizes
| Size | Neck / Taper Diameter | Typical Vessel |
|---|---|---|
| NS 14/23 | 14 mm top, 23 mm taper length | Small flasks, burettes, test apparatus |
| NS 19/26 | 19 mm top, 26 mm taper length | Standard round-bottom and Erlenmeyer flasks |
| NS 24/29 | 24 mm top, 29 mm taper length | Reagent bottles, larger flasks |
| NS 29/32 & 34/35 | 29 mm and 34 mm tops | Large flasks, reactors, condensers |
| Bung 000 – 12 | ≈ 10 – 90 mm neck bore | Bottles, bottles with tubing ports |
Choosing the Right Stopper
- Match the joint marking — A ground-glass stopper must carry the same NS number as the vessel neck; mixing NS 19 with NS 24 will leak or jam. Order stoppers together with their flasks and bottles so the tapers are matched.
- Match the chemistry — Choose PTFE for solvents, acids and anything aggressive; ground glass for aqueous and volumetric work; avoid glass joints with strong alkali, which etches and seizes them.
- Match the temperature — Silicone for autoclaves and hot baths, rubber for ambient general use, PTFE where both heat and chemical resistance are needed.
- Think about ports — One- and two-hole bungs let you pass tubing, thermometers or electrodes through a stopper without a separate adapter.
Handling and Storage Practice
Insert a ground-glass stopper with a gentle twist rather than pressure, and never force a stopper that resists — a mismatched taper is the usual cause. Store glass stoppers loosely seated, or with a thin paper strip between stopper and neck, so the joint cannot freeze during storage; a frozen joint often ends with a broken flask. Keep rubber and silicone bungs away from direct sunlight and UV lamps, which harden them long before their useful life is over. Clean stoppers with warm water and mild detergent, rinse with distilled water and dry thoroughly before storage to prevent mould growth inside tubing ports.
Why Choose JWRESEARCH for Stoppers in Singapore?
- Complete range — Ground-glass, PTFE, silicone, rubber and cork stoppers in every common NS size and bung number.
- Accurate tapers — Standard NS joints and consistent bung dimensions that seal the first time.
- Matched supply — Order stoppers, flasks, bottles and tubing ports together for guaranteed fit.
- Fast local delivery — Quick dispatch across Singapore for QC labs, universities and research institutes.
JWRESEARCH supplies ground-glass, PTFE, silicone, rubber and cork stoppers and bungs to laboratories across Singapore. Contact us for sizes and volume pricing.
📞 +65 8039 3660 | ✉️ SINGAPORE@JWSHY.COM
🌐 www.jwresearch.cn
Frequently Asked Questions
Q: How do I know which stopper size fits my flask or bottle?
For ground-glass joints, use the standard NS (also written ST or B) number — NS 14/23, 19/26, 24/29, 29/32 or 34/35 — printed on the neck of the vessel. The two figures are the top and bottom diameters of the taper in millimetres, so a stopper must carry the identical NS marking to seat properly. For unground bottles, measure the inside diameter of the neck in millimetres and order a rubber, silicone or cork bung of the same nominal size; bungs share a common numbering system (000 to 12) that corresponds to neck diameter.
Q: Should I use PTFE or glass stoppers for solvent bottles?
PTFE stoppers are the safer default for solvents and corrosive liquids because PTFE is almost universally chemically inert and will not seize in the joint the way glass can. Ground-glass stoppers give a perfect, leak-free seal for aqueous and non-alkaline solutions and are the classic choice for volumetric flasks and reagent bottles, but they must never be used with strong alkalis — which etch and fuse the joint — and should be stored loosely inserted, never forced, to avoid freezing shut. Many labs keep both: PTFE for aggressive chemistry, glass for precise volumetric work.
Q: What is the temperature limit of silicone versus rubber stoppers?
Silicone stoppers are the high-temperature option, serviceable from roughly -60 °C to 200 °C, and they resist ageing and steam, which makes them good for autoclaves and hot-water baths. Natural and nitrile rubber bungs are softer and cheaper but are generally limited to about 100 – 120 °C and harden or crack with repeated autoclaving. For cryogenic work use silicone or a dedicated low-temperature bung, never cork, which becomes brittle near -80 °C.
Q: How should I store and clean stoppers to keep them sealing?
Rinse stoppers with warm water and a mild detergent, then with distilled water, and dry them before storage. Never use abrasive cleaners or strong alkali on glass joints. Store ground-glass stoppers loosely inserted or with a thin paper slip between stopper and neck so the joint cannot seize; keep rubber and silicone bungs out of direct sunlight and away from ozone sources such as UV lamps, which accelerate cracking. Inspect bungs regularly and discard any that are glazed, cracked or permanently deformed.