What is the use of the hub drain? What fixture thus it served

What is the use of the hub drain? What fixture thus it served

Basically a hub drain is a round drain that is completely open, no basket strainer or drain cover. It is used to receive indirect condensate drainage. We typically use them for condensate drainage of refrigerated cases that you see in the supermarket. Is that what you wanted to know? Regards, Ton

Yep, usually used for indirect waste or air gap purposes.