Glass tube fuses are safety devices used in electrical circuits to protect against overloads and short circuits. They consist of a glass tube filled with a metal wire or filament that melts when excessive current flows through it, breaking the circuit and preventing damage to electrical components. These fuses come in various sizes and ratings, making them suitable for different applications, from household appliances to industrial machinery. When a fuse blows, it must be replaced with a new one of the same type and rating to restore functionality and ensure safety in the electrical system.