Reduction Adapters, Reducing Interchangeable Joints

Quick Answer: A reduction adapter is a short piece of glass that steps a ground joint down in size: its wide cone enters a large neck, and a narrower socket above it accepts a smaller cone. That lets a component such as a thermometer adapter or small condenser sit in a flask neck of a bigger size.

Stepping Down a Joint Size

Laboratories often own flasks with large necks and accessories with smaller joints. This fitting handles exactly that case. The wide cone at its base goes into the big socket of the flask or still head, and the narrow socket at its top receives the smaller cone of whatever must be fitted. Typical examples are a small reflux condenser on a large flask during a reaction that gives off little vapour, a thermometer adapter or stopper in a wide side neck, and a dropping funnel with a small joint on a large reaction flask.

The opposite fitting, with a small cone and a large socket, is the expansion adapter. The two names are easily confused, so describe the adapter by its ends: the cone size that goes down into the vessel and the socket size that receives the next piece. The sizes of this item are not given in the title.

Every adapter adds a joint and some height to the stack. A small condenser perched on a large flask through an adapter is top-heavy, so clamp the condenser as well as the flask.

Care & Handling

• Grease or sleeve both joints, since two joints in place of one give the set twice as many places to leak.
• Clip both joints; the smaller upper one in particular can pull out under the weight of a condenser.
• Separate the adapter from both partners after use, as a joint left assembled with basic solution can seize.

Applications

• Fitting a small condenser or air condenser to a large round-bottomed flask
• Placing a small-cone thermometer adapter or stopper in a wide flask neck
• Using semi-micro accessories with standard-size flasks
• Combining glassware bought at different times with different joint sizes

Specifications

Why Choose LabEquip

Labs whose glassware has grown piece by piece, with mixed joint sizes, rely on fittings like this to keep older and newer items working together. LabEquip lists them in its chemistry lab equipment range; state both joint sizes on the contact page.

Frequently Asked Questions

Is this the same as an expansion adapter?

No, it does the reverse job. This fitting lets a smaller component sit in a bigger neck; an expansion adapter lets a bigger component sit on a smaller neck. Naming the cone size and the socket size avoids any mix-up.

How are the sizes of this adapter described?

By its two joints, each written as the wide-end diameter and ground length in millimetres, such as 24/29, or as a B number. Both must match the pieces being joined.

Does using an adapter affect the seal?

It adds a second joint, so there are two surfaces that must seal. Lightly greased or fitted with PTFE sleeves, the pair holds as well as a single joint does.

Can I use it for vacuum work?

Yes, if both joints are greased and clipped and the glass is undamaged. Test the stack for leaks before heating.

Why not just buy a flask with the right neck?

For regular use that is often better. The adapter is the practical answer when existing glassware must be combined, or when one flask is used with accessories of several sizes.

Can the adapter carry a heavy condenser?

Not on its own. Clamp the condenser to the stand so the adapter only locates it; the smaller joint is the weak point of the stack.

Last Updated: September 2026