There are various types of contactors, and each type will have its own set of specifications depending on your application. Some key specifications are

• AC Contactor or DC Contactor with coils including 12 V, 24 V, 48 V, 110 V, 240 V, 400 V, and 440 V.
• Reversing or non-reversing functionality.
• AC3 and AC1 categories
• Contactors with 2 poles, 3 poles 4 poles, and even 8 and 10 pole variants.
• Various contact configurations.
• IEC standards