How much should I tighten brew head screen screw?

I removed the center screw holding the brew head screen, and cleaned the screen and exposed surface of the brew head. Then I put the brew head screen back in place with the center screw. I am unsure how much to tighten the center screw, as I am concerned that tightening it until the screw stops turning may tighten it too much and block water flowing from the center of the brew head. Can someone please tell me how much I should tighten the brew head screen center screw?