Turnover Flange Septa, for Test Tube

Quick Answer: Turnover Flange Septa for Test Tube are rubber stoppers with a thin flange that is folded down over the outside of a test tube’s rim after insertion, so the tube is sealed while a syringe needle can still pierce the centre to add or remove liquids or gases.

How a Turnover Septum Seals a Tube

The septum has three parts: a plug that fits inside the mouth of the tube, a thin central diaphragm, and a skirt above it. After the plug is pushed in, the skirt is folded down so that it grips the outside of the tube like a sleeve. That double contact, inside and outside the rim, holds the septum firmly even when the tube is shaken, warmed gently or held under slight pressure.

Once fitted, the tube is closed to air but still accessible through the diaphragm with a syringe needle. This is how chemists keep small amounts of air- or moisture-sensitive solutions under nitrogen or argon, how gas can be sampled from the headspace of a sealed fermentation tube, and how students collect gases from small-scale reactions without opening the vessel.

The test tube version is sized to the rim of plain tubes; the companion Turnover Flange Septa, for Socket is sized instead for ground-glass joints on flasks. Measure the tube mouth before ordering, because a septum that is slightly too large will not hold its seal.

Specifications

Uses in the Lab

• Keeping small samples under nitrogen or argon in test tubes.
• Syringe transfer of reagents into sealed reaction tubes.
• Headspace gas sampling from sealed fermentation or culture tubes.
• Collecting gas from micro-scale reactions in school chemistry.

Care & Handling

• Use the finest needle that suits the job and pierce a slightly different spot each time to extend septum life.
• Replace the septum after many punctures or if the rubber hardens, as the seal then leaks.
• Keep spare septa sealed and away from light, heat and ozone sources such as electric motors.
• Check solvent compatibility; natural rubber swells in many organic solvents.

Why Choose LabEquip

Research labs, organic chemistry courses and microbiology departments working with sealed tubes buy turnover septa as routine consumables. LabEquip supplies them with the rubber goods in General Lab Products; send the tube diameters via the contact page to get the right size.

Frequently Asked Questions

What does ‘turnover flange’ mean on a septum?

It refers to the thin skirt at the top of the septum, which is turned down over the outside of the tube after insertion. This grips the rim from outside as well as inside, giving a secure seal.

How is a turnover septum fitted to a test tube?

Push the plug into the tube mouth with the skirt pointing up, then fold the skirt down over the rim. Gentle pressure with the thumb all round smooths it into place.

How many times can a septum be pierced?

It depends on the needle size and the rubber. Fine needles cause less damage, but every puncture weakens the diaphragm, so replace septa once the seal becomes unreliable.

Can the septum be used with organic solvents?

Natural rubber swells in many solvents, especially hydrocarbons and chlorinated solvents. Limit contact to the vapour space, or choose a septum material suited to the solvent.

What is the difference between the test tube and socket versions?

The test tube septum fits a plain tube rim. The socket version is sized for the ground-glass joint sockets of flasks and adapters.

Can the septa be autoclaved?

Some rubber septa tolerate autoclaving, while others harden or deform. Check the rating of the septum material before sterilising, and let it cool before use.

Last Updated: September 2026