WE got mulled windows, but they didn't come with any screws. Installers are here now --- need an immediate answer for exactly what kind of self-tapping screws we need to install the mull -- how long, guage, etc.

Your installers should already know this information according to code, if they dont thats a red flag, stop immediately and hire another company.

The answer needs a lot more questions to be answered like what substrate the screws are going into best thing to do is to call PGT rep or call PGT directly I don't see wine your installers don't know