Connectors are broadly classified by their application and design, including circular connectors, rectangular connectors, and terminal blocks. Circular connectors are rugged and often used in industrial automation for their reliable sealing against dust and moisture. Rectangular connectors, or heavy-duty connectors (HDCs), are ideal for transmitting power and signals in machinery due to their high pin density and modularity. Terminal blocks provide a simple, secure way to terminate and distribute wires within control panels.