Glass Stoppers

Glass stoppers are manufactured to standardised taper sizes (NS 7, NS 10, NS 14, NS 19, NS 24, NS 29, NS 34, NS 45) matching vessel neck designations. Always match the stopper size to the vessel neck designation. Glassware is labelled with its neck taper size.

Flat-top solid stoppers are used for general-purpose bottle sealing. Ground glass stoppers with a polished tapered surface provide an airtight seal for volumetric flasks and precision glassware. Hollow-bore stoppers are used in burettes and separating funnels where liquid flow control is required.

Borosilicate glass stoppers are compatible with nearly all laboratory chemicals including strong mineral acids (except HF), alkalis, and organic solvents. For hydrofluoric acid or strong caustic solutions at elevated temperatures, use PTFE-sleeved or PTFE stoppers instead.

Ground glass stoppers can become stuck after contact with alkaline solutions due to silicate deposit formation. Lightly grease the taper with silicone grease before use with alkaline solutions. If a stopper has seized, gentle warming in warm water and firm twisting usually releases it. PTFE-sleeved stoppers eliminate direct glass-to-glass contact.

The stopper size is determined by the neck taper designation marked on your glassware (NS 14, NS 19, NS 24, NS 29). Match the stopper number to the vessel number. Standard volumetric flasks typically use NS 14 or NS 19 stoppers; larger flasks and reagent bottles use NS 24 to NS 34.

Yes. Borosilicate glass stoppers are compatible with most laboratory acids, organic solvents, and halogens, and are preferred over plastic closures for strong acids. The exception is hydrofluoric acid, which requires PTFE closures. For concentrated sodium hydroxide, use PTFE-sleeved stoppers to prevent joint seizing.

Warm the neck of the vessel in warm water for a few minutes to expand the glass slightly, then twist and pull gently. A rubber mallet tapped lightly sideways can break the seal. Avoid excessive force. Prevent seizing by using a thin film of silicone grease on the taper when working with alkaline solutions.

Standard stoppers have a plain polished taper for general reagent bottle sealing. Ground glass stoppers have a precision-ground surface creating a gas-tight seal when matched to a ground-glass neck. Ground glass stoppers are required for volumetric flasks and apparatus where vapour-tightness or vacuum is essential.

Yes. Borosilicate glass stoppers can be autoclaved at 121 degrees Celsius. Remove stoppers from bottles before autoclaving to allow steam penetration and prevent pressure build-up, then replace once the contents have cooled to avoid contamination.