When using an electromagnet, what must be affixed to it?

The correct choice emphasizes the importance of having durable identification affixed to an electromagnet, indicating its size and rated capacity. This information is crucial for ensuring safe and effective operation. The rated capacity specifies the maximum weight the electromagnet can handle, which is vital for both the safety of the operator and the integrity of the loads being lifted. Using an electromagnet beyond its rated capacity can lead to equipment failure, accidents, and potential injuries.

Having the correct size identification aids in properly matching the electromagnet to the loads being lifted, enhancing both functionality and safety. This ensures that operators can quickly and easily ascertain the electromagnet's capabilities at a glance, which is essential when working in dynamic and potentially hazardous environments.

While other options provide valuable information for safety and communication, they do not address the immediate need for identifying the electromagnet's specifications directly relevant to its use and operational safety.