Cone Adapters, Straight Connection

Quick Answer: A straight cone adapter is a glass fitting with a ground-glass cone at one end and a straight tube at the other, in line with the joint. It lets rubber or plastic tubing be connected to any socket of matching size for gas, vacuum or vent lines.

The Simplest Joint-to-Tubing Link

Many ground-joint assemblies need a point where rigid glass meets flexible tubing, and this fitting is the most direct way to make it. Pushed into a socket, it continues the axis of the joint as a tube over which tubing can be slipped. Because it adds no bend and little height, it suits side necks that already point sideways, the outlet of a vacuum receiver or a horizontal socket on a manifold.

Straight adapters are also used where a set-up needs a slow bleed of gas, for example to pass nitrogen over a reaction, and on top of a reflux condenser when tubing can run straight up to a support before turning down to a trap. Compared with a bored rubber bung and glass tube, a ground cone gives a cleaner, more solvent-resistant seal in a ground-glass socket.

Joint size and tube diameter are not stated in the listing. For connections that must be shut off at the joint, the cone adapter with stopcock is the related option.

Specifications

Care & Handling

• Choose tubing whose bore fits snugly over the tube end; loose tubing leaks and very tight tubing is hard to fit.
• Keep the cone free of grit, which scratches ground surfaces and spoils the seal.
• Clip the cone into its socket wherever tubing could pull it loose.
• Rinse the bore after use with a solvent that removes any condensed residue.

Applications

• Gas inlet into a horizontal side neck of a two- or three-neck flask
• Vacuum or vent connection on the outlet socket of a receiver
• Replacing a bung and glass tube in a ground-joint socket for better solvent resistance
• Linking a set-up to a bubbler that shows the gas flow

Why Choose LabEquip

Teaching and research labs building ground-joint sets usually keep several straight cone adapters on hand for gas and vacuum lines. They can be ordered from LabEquip’s chemistry lab equipment range; tell us the joint size and tubing bore on the contact page.

Frequently Asked Questions

When is a straight cone adapter preferable to an angled one?

When the socket already points sideways or downwards, a straight adapter lets the tubing continue in the same direction without an extra bend. On an upright neck, an angled adapter usually gives a tidier, less strained tubing run.

Why use a cone adapter instead of a rubber bung with a tube?

A ground cone seals in a matching socket without rubber, which organic solvents can swell or dissolve. It also avoids fragments of rubber entering the reaction and is easier to remove and clean.

What tubing fits the adapter?

Rubber, silicone or plastic tubing with an internal bore that fits snugly over the glass end. For vacuum work, use thick-walled vacuum tubing so it does not collapse.

Can the straight cone adapter carry corrosive gases?

Glass resists most corrosive gases well. The limiting parts are usually the tubing and any grease on the joint, so choose tubing and sleeve materials that suit the gas.

How do I know the cone size?

Ground joints are normally marked with their size on the glass. Match that size to the socket, such as the side neck of your flask, before ordering.

Can I use one adapter on different flasks?

Yes, as long as each flask has a socket of the same joint size. That interchangeability is the main advantage of standard ground-joint glassware.

Last Updated: September 2026