Glass Fuses which are safety devices used in electrical circuits. Key information about glass fuses:

Function: They protect electrical circuits from overcurrents, preventing damage to equipment and reducing the risk of fire. 
Construction: They consist of a glass tube enclosing a metal filament that melts and breaks the circuit when the current exceeds a specific level. 
Types: They come in various sizes (e.g., 5x20mm, 6x30mm) and current ratings (e.g., 0.5A to 30A). 
Usage: Commonly found in appliances, electronics, and older vehicles. 
Replacement: Always replace a blown fuse with an identical type to avoid hazards. 
Speed: Fuses can be fast-blow or slow-blow, depending on the application. 
Inspection: The transparent glass allows for easy visual inspection to check if the fuse has blown.