The pump’s info sticker doesn’t have much info to tell:

Besides showing the manufacturer’s logo, the sticker just tells you that it’s a pump and that’s all. And there is also a scale that shows the level of the coolant. At the top of the pump, under a metal cap and a rubber plug, there’s a hole which is probably meant for adding coolant into the system.

The plug sits rather tight in its hole:

So, the metal cap even seems an unnecessary precaution measure.