Glass Adapters for Laboratory Systems

Ground glass joints follow ISO standard sizes: B10, B14, B19, B24, B29, and B40. The number indicates the inner diameter at the widest point of the joint in millimetres. Always verify the joint sizes on both connecting pieces before ordering an adapter. Mismatched sizes will not seal, regardless of how tightly you apply grease.

Bent adapters change direction; straight adapters extend a connection; reducing adapters bridge different joint sizes; vacuum adapters add a side port for tubing; Claisen adapters create a two-port branch for simultaneous operations; cow adapters allow multiple fraction collection without disturbing the still head. Match the adapter to the specific function it needs to perform in your assembly.

For reduced-pressure distillation or vacuum filtration, apply a thin layer of high-vacuum silicone grease to the ground glass joints to create an airtight seal. Inspect all adapters for chips, hairline cracks, or star fractures before applying vacuum. Any defect will cause a leak and prevent the system from holding pressure. Wipe joints clean before greasing to prevent contamination of the product.

Borosilicate glass adapters resist most laboratory acids, alkali solutions, and organic solvents. They are not suitable for hydrofluoric acid or prolonged exposure to hot, concentrated sodium or potassium hydroxide, both of which etch and weaken glass over time. For such applications, PTFE-sleeved joints or all-PTFE fittings are the correct choice.

Ground glass joints are precisely machined tapered connections on laboratory glassware. The inner (socket) and outer (cone) surfaces are ground to a smooth, matching taper so that two pieces fit together snugly with glass-to-glass contact. This creates a near-airtight seal without any clamps or adhesives, and allows components to be assembled, disassembled, and recombined quickly. A light application of vacuum grease or PTFE tape on the joint improves the seal for vacuum or pressure work.

The letter B stands for the ISO/DIN standard for ground glass cone joints (Kegel in German). The number is the outer diameter of the joint cone at its widest point, measured in millimetres. So a B14 joint has a 14 mm maximum outer diameter, a B24 joint has 24 mm, and a B40 has 40 mm. When buying an adapter, both the socket and cone must share the same number to fit together correctly.

Glass joints seize when chemicals dry inside the joint or when glassware is left assembled for long periods, particularly after alkaline solutions have been used. To prevent seizing: always disassemble joints promptly after use, rinse with appropriate solvent, and apply a very thin film of silicone vacuum grease before reassembling. If a joint has already seized, soak it in warm water or acetone and apply gentle sideways pressure. Never force the joint apart with a direct pull, as this can crack the glass.

Yes, provided the joints are in good condition and correctly greased. Borosilicate glass can withstand pressures well below atmospheric (vacuum conditions) and is the standard material for reduced-pressure distillation setups. Inspect all adapter joints for chips or cracks before pulling vacuum, as any defect will prevent the system from holding pressure and may cause implosion under deep vacuum. Use vacuum-rated silicone or fluorinated grease on the joints.

A bent adapter simply changes the angle of a connection. It has one inlet and one outlet and is used to redirect glassware to fit a particular stand or spatial arrangement. A Claisen adapter has one inlet (bottom joint, connects to the flask) and two outlets (two upper joints), creating a Y-shape that allows two separate accessories to be fitted to a single flask simultaneously, such as a condenser and a dropping funnel, or a thermometer and a gas inlet.