Cone, Single, Interchangeable

Quick Answer: A single interchangeable cone is one male ground-glass joint: a tapered, ground section of glass, typically with a plain tube (shank) extending from it. It fits into any socket of the same standard size, and is used by glassblowers and technicians to build, extend or repair apparatus.

What a Single Cone Is For

Ground-glass joints come in pairs: the tapered cone, which is the male part, and the socket, which receives it. A single interchangeable cone is the male half sold on its own. In most laboratories it is a component rather than finished apparatus: a glassblower fuses the shank onto a flask neck, tube or custom vessel to give it a standard joint, or replaces a broken cone on a condenser or adapter instead of discarding the whole piece.

Because the taper and diameter follow a standard, a new cone fits every socket of the same nominal size. Sizes are commonly written as two numbers, the diameter at the wide end and the ground length in millimetres, or as a code such as B19 or B24. The listing does not state the size or the form of the shank, so these should be specified.

In teaching, a spare cone is a simple way to show how a ground joint seals. A lightly greased cone turned in its socket becomes clear where the ground surfaces meet, and an even, transparent band is the sign of a good seal. Matching sockets and paired joints are listed as interchangeable joints.

Care & Handling

• Apply grease as a thin ring around the upper third of the cone only, then seat and rotate; excess grease spreads into the apparatus.
• Do not leave a cone seated for long in a socket that holds alkaline solution, which etches ground glass and can fuse the joint.
• Store single cones wrapped separately so ground surfaces do not scratch against each other.
• Anneal any cone fused to new glass, in an annealing oven or flame, to relieve stress at the seal.

Applications

• Replacing a broken cone on a condenser, adapter or stopper-type fitting during glass repair
• Adding a standard joint to a custom flask or tube in a glassblowing workshop
• Making up adapters for non-standard apparatus in research labs
• Demonstrating how ground joints seal when greased and seated

Specifications

Why Choose LabEquip

Glassblowing workshops, university technicians and labs that repair their own glassware keep single cones in the sizes they use most. LabEquip stocks this component with its chemistry lab equipment; send the joint size and quantity through the contact page.

Frequently Asked Questions

What is the difference between a cone and a socket?

The cone is the male part of a ground joint, tapered and ground on the outside. The socket is the female part, ground on the inside to receive a cone of the same size. Together they form a sealed, removable connection.

What does interchangeable mean for ground joints?

It means every joint of a given nominal size shares the same taper and dimensions, so any cone fits any socket of that size from any maker. Parts can be swapped, replaced or combined without custom fitting.

How do I read a joint size such as 24/29?

The first number is the diameter at the wide end of the ground zone in millimetres, and the second is the length of the ground zone. A 24/29 cone fits any 24/29 socket.

How should a cone be greased?

Apply a thin ring of grease around the upper part of the cone, insert it, and turn it a little until the joint looks clear all round. A clear, even band shows a good seal; streaks show gaps.

Why do ground-glass joints seize?

Joints stick when grease hardens, when solids dry between the surfaces, or when alkaline solutions etch the glass. Separating joints after each use and keeping strong alkali out of greased joints prevents most seizures.

Can a single cone be fitted to existing apparatus?

Yes, by a glassblower, who joins the cone’s shank to the apparatus in a flame and then anneals it. It is a common way to repair a broken joint instead of replacing the whole piece.

Last Updated: September 2026