schrader valve is the fuel pressure test port and its named so due to the internal mechanism that allows you to press in the valve and have a open line or let go of the valve and have it seal perfectly...

on the crossfire it is a standard 4AN fitting ... for those that are wondering, using a 1 dollar tool you can unscrew the inernal schrader valve and have a nice 4AN attachment point off the fuel rail to supply things like nitrous kits and extra injectors...