How do I know which thread size my bottle needs?

Thread size is written as a number followed by mm and refers to the outer diameter of the bottle neck, not the cap. Common laboratory sizes are GL14, GL18, GL25, GL32, GL45 and GL45 wide-mouth, plus 13-425, 15-425, 20-400, 24-400 and 28-400 for vials and small bottles measured in mm with the thread style after the hyphen. Measure the neck across its outside edge with a calliper, or read the number moulded on the bottle. A GL45 cap will not fit a GL32 neck, and forcing a mismatched cap damages the thread and destroys the seal. When in doubt, send us the bottle part number and we will match the correct cap and liner.

What is the difference between a lined and an unlined cap?

An unlined cap seals by pressing the cap material directly against the bottle rim, which works for aqueous solutions that are not sensitive to solvents or gases. A lined cap carries a separate disc of PTFE, silicone, EPDM, butyl or a laminated combination that forms the real sealing surface. The liner decides chemical compatibility and the barrier to vapour, oxygen and moisture. PTFE-faced liners resist almost all chemicals and are the default for organic solvents and acids. Silicone liners are soft and compressible and seal well at low temperature. EPDM and butyl are used for aqueous and steam applications. Choose the liner from the contents and the temperature, not from the convenience of the cap.

When should I use a phenolic or aluminium cap instead of polypropylene?

Polypropylene is the general-purpose choice: chemically resistant, autoclavable and cheap, which is why it is the default for most laboratory bottles and reagent containers. Phenolic caps are hard thermoset plastic that resist high temperature and steam better and are often used on media bottles and in autoclave cycles where a firmer seal is wanted. Aluminium caps and crimp seals are used where a thin, pilfer-proof or high-barrier closure is needed, such as sample vials, headspace and chromatography work, and they suit automated capping machines. If your process involves repeated autoclaving or a very aggressive solvent, move away from plain polypropylene and choose the material and liner combination the application validates.

What closures does JWRESEARCH supply in Singapore?

JWRESEARCH supplies laboratory closures in Singapore including polypropylene screw caps, phenolic caps, aluminium screw caps and crimp caps, septum caps and open-top caps, in GL and vial thread sizes. We stock matching liners in PTFE, silicone, EPDM and laminated formats, plus septa for chromatography and headspace work. Because caps and liners are high-turnover consumables, we quote volume pricing for contract laboratories, hospitals and industrial labs and hold local stock for replenishment on request. Tell us the bottle or vial you use and the contents, and we will match thread, material and liner.

Screw Caps and Closures Singapore

Published: {{NEW_ARTICLE_DATE}} | By JWRESEARCH | Category: Laboratory Consumables

A cap is a small part with a large job: it keeps the contents in, the environment out, and the label honest. Choose the wrong thread and it will not seat. Choose the wrong material or liner and it will leak, evaporate a solvent, or be attacked by the very chemical it is meant to contain. The three variables that decide everything are thread size, cap material and liner.

At JW RESEARCH SUPPLY, we supply screw caps, closures, liners and septa to research institutions, contract laboratories and industrial quality-control labs across Singapore. This guide explains how to match a cap to a bottle, how liners change sealing behaviour, and how to store and reuse closures safely.

Closure Types Compared

Type	Material	Typical Use
General screw cap	Polypropylene	Reagent bottles, media and general storage
Phenolic cap	Thermoset phenolic	Media bottles, autoclave and steam cycles
Aluminium cap	Aluminium with liner	Sample vials, high-barrier and pilfer-proof work
Crimp cap	Aluminium, open-top	Headspace and chromatography vials
Septum cap	Cap plus silicone or PTFE septum	Repeated injection and sampling
Vented cap	Polypropylene with PTFE vent filter	Sterile culture and gas exchange

Specification Reference

Parameter	Typical Value	Notes
Thread sizes	GL14, GL18, GL25, GL32, GL45; 13-425, 15-425, 20-400, 24-400	Match to the bottle neck outside diameter
Cap materials	Polypropylene, phenolic, aluminium, PTFE	Material sets chemical and temperature limits
Liner materials	PTFE, silicone, EPDM, butyl, laminated	Liner is the real sealing surface
Autoclave limit	About 121 °C for PP and phenolic	Loosen caps during sterilisation
Liner thickness	Generally 0.5–2 mm	Thicker liners tolerate uneven rims
Working temperature	−40 to +140 °C by material	Check the liner, not just the cap
Pack format	Bag of 100, case of 500–1000	Case pricing for high-volume laboratories

Matching the Thread

Thread size describes the neck, not the cap. A GL45 cap fits a 45 mm neck outside diameter; a GL32 cap will not thread onto it and a GL45 cap will spin on a GL32 neck without sealing. Vial ranges use a different convention — 13-425, 20-400, 24-400 — where the first number is the neck diameter in millimetres and the suffix is the thread style, so a 13-425 cap and a 13-425 vial must be paired.

The reliable way to check is to measure the neck across its outside edge with a calliper, or to read the moulded number on the bottle. Never force a cap that does not start by hand: cross-threading chews the neck and the bottle will never seal again. If you are matching caps to an existing bottle range, send us the bottle part number and we will confirm thread, material and liner in one step.

Choosing the Liner

The liner is the part that actually seals, and it is the part most often overlooked. PTFE-faced liners resist nearly every solvent and acid and are the safe default for organic chemistry and reagent storage. Silicone liners are soft, compressible and stay flexible at low temperature, which suits freezers and cold rooms. EPDM and butyl liners seal well with water and steam and are common on media and buffer bottles. Laminated liners combine a soft backing with a PTFE face so the cap compresses easily and the contents only ever touch PTFE.

Decide the liner from the contents, the temperature and the required shelf life. Aqueous buffer in a cool room and dichloromethane on a bench need different liners even if the bottle and cap are identical. When a solvent climbs out of a sealed bottle, the loss is usually the liner, not the thread.

Sterilisation and Reuse

Step	Action	Why It Matters
Before autoclaving	Loosen the cap a quarter turn	Prevents pressure build-up and cracked bottles
After autoclaving	Retighten once cool, in a clean area	Restores the seal without drawing in air
Reuse	Inspect thread and liner before every refill	A scored liner leaks even with a good cap
Solvent service	Replace liners that have swollen or stiffened	Degraded liners contaminate and leak
Storage	Keep caps dry and out of direct sun	Heat distorts polypropylene and ages liners
Trace work	Use a fresh cap and septum per batch	Prevents carry-over in sensitive analysis

Reusing caps is normal in a busy laboratory, but it is only safe while the thread is clean and the liner is intact. A liner that has swollen, hardened or picked up colour has already failed; replacing it costs far less than repeating an analysis.

Ordering Checklist

Thread size confirmed against the neck, not guessed from the cap
Cap material matched to temperature and chemical exposure
Liner material chosen from contents and required shelf life
Septum and open-top caps specified for sampling and injection
Pack and case quantity against monthly consumption, plus spare
Replacement liners ordered with the caps for reuse programmes

Send us the bottle or vial you use and what goes into it, and we will match thread, cap material and liner so one order keeps every bottle in the laboratory sealed and labelled.

Contact JWRESEARCH

JW RESEARCH SUPPLY — laboratory equipment and consumables, Singapore.
Telephone / WhatsApp: +65 8039 3660
Email: SINGAPORE@JWSHY.COM
Website: www.jwresearch.cn