Purpose of threaded port?

[fastback4]

Thanks You........Tom

[1meanz]

its a bleeder screw, whenever you change tstats, or flush your anti freeze ect, it gets the air out of the system, without doing this you will not have heat, and the car can run hot.

[fastback4]

What is the purpose of this threaded port at the upper radiator hose area on my 1997 3.1 MC?
Regards........Tom