A solid glass stopper, penny head, is a type of laboratory glassware used to close and seal containers, such as flasks or bottles. It is typically made of solid glass and is cylindrical in shape, with one end that fits into the neck of the container and the other end that is flat and rounded, resembling a penny.

The stopper is inserted into the container to create an airtight seal, which is necessary for many chemical experiments where air or moisture must be excluded. The solid glass material provides a durable and chemically resistant seal, making it a reliable choice for laboratory use.

The stopper is available in a range of sizes to accommodate different neck sizes of containers and its flat and rounded design provides a stable and secure grip when inserting and removing the stopper.