Cork Stopper, Extra Soft, One Hole

Quick Answer: This one hole cork stopper is an extra-soft tapered rubber stopper with a single bored hole through its centre. It seals a test tube, boiling tube or flask while holding one piece of glass tubing, a thermometer or a glass rod.

Soft Rubber, One Opening

In Indian laboratory supply the word cork is widely used for any tapered stopper, and this extra-soft series is rubber; the solid version is listed as the Rubber Cork Stopper, Extra Soft, Solid. The single hole turns a closed vessel into a simple piece of apparatus: a thermometer held in a boiling tube for a cooling-curve experiment, a delivery tube leading gas from a heated tube to a trough of water, or a short glass tube carrying a rubber valve or airlock.

A softer compound seals with less pushing force and grips glass necks that are slightly out of round or worn, which is useful with thin-walled tubes that can crack if a hard stopper is forced in. The trade-off is that a soft stopper is easier to push in too far and can tear if glass tubing is forced through the hole. For an inlet and an outlet in one stopper, see the two hole version.

Care & Handling

• Wet the glass tube with water or a drop of glycerol, wrap it in a cloth and ease it through the hole with a gentle twist, holding it close to the stopper.
• Never push glass through a stopper with the palm pressed on the end of the tube.
• Keep rubber stoppers away from organic solvents such as ether, chloroform and petrol, which swell rubber.
• Remove glass tubing after use so the stopper does not grip it permanently as it ages.

Applications

• Holding a thermometer in a boiling tube for melting and cooling-curve experiments
• Fitting a delivery tube to a test tube or flask to collect gas over water
• Carrying a glass tube and rubber valve for fermentation or anaerobic set-ups
• Sealing a boiling tube with a glass rod or capillary for demonstrations

Specifications

Why Choose LabEquip

Schools and colleges use one hole stoppers in almost every gas collection and heating practical, so they are usually ordered across several sizes. LabEquip lists this soft grade in the General Lab Products range; send the neck sizes of your tubes and flasks through the contact page.

Frequently Asked Questions

Is this stopper made of cork or rubber?

It is rubber. In Indian laboratory supply the word cork is used for any tapered stopper, and the extra soft series is rubber, as the solid version’s listing shows.

What size should I choose for my tube?

Pick the size whose narrow end slips into the neck and then seats with about one-third to one-half of the stopper inside. If it sinks deeper, go up a size; if it barely enters, go down a size.

How do I fit a thermometer through the hole safely?

Wet the thermometer stem with water or glycerol, hold it close to the stopper with a cloth around your hand and twist it through gently. Never force it.

Why choose an extra soft stopper?

It seals with less force and grips worn or slightly uneven glass necks. It is also gentler on thin-walled tubes that could crack under a hard stopper.

Can it be used with organic solvents?

Rubber swells and softens in many organic solvents. For those, a cork, glass or PTFE closure is more suitable.

How do I remove a glass tube that is stuck in the stopper?

Lubricate around the tube and twist gently. If it will not move, slide a cork borer just larger than the tube over it to free it, or cut the stopper away rather than risk breaking the glass.

Last Updated: September 2026