This connection with the screw in it was designed to "T" into the return line to the fuel tank. Its purpose was to help with hard starting vapor lock. The spring and disc you refer to in your picture is a check valve to allow fuel/vapor/bubbles to flow in only one direction. It's swedged in, and is not supposed to come out. However, a lot of them end up clogging up so removal is often necessary. It can be reinstalled safely by further swedging the already swedged tabs in some more. And no, there is no ball bearing as part of the check valve. Just the disc and spring .
Baron, I've never seen one without this spring and disc. Is this check valve something that you don't clean when you rebuild your pumps?