Electrical Switch

A "square holder" is not a standard term in the context of lighting fixtures or electrical components. It's possible that you may be referring to a specific type of lighting fixture or holder with a square shape or design, but without more context or details, it's challenging to provide specific information.

A Single Pole Miniature Circuit Breaker (MCB) is a type of circuit protection device commonly used in electrical distribution panels to safeguard individual electrical circuits. MCBs are designed to automatically disconnect the electrical circuit they protect when an overcurrent condition occurs, such as a short circuit or an overload. The term "single pole" refers to the number of conductors or phases the MCB can interrupt, and it typically corresponds to a single-phase circuit.