The ZA185-51 is a 440/480V AC replacement coil for A-Line contactors, specifically the A145 through A185 frame sizes. It's a service part — you swap it in when the original coil fails or when a line voltage change requires a different control voltage.
The 480V AC control coil is wound for 440/480V AC line-to-line pickup. It mounts into the A145 and A185 contactor frames — same footprint, same terminal layout.