Margo, If your focuser is the same as mine (8" Dob), this is what you have.
There is one screw for regular (1.25") EPs. You've obviously found this one..
Then there is two identical screws 90 degrees apart, just behind the EP screw. These are for 2" EPs, and are actually holding a 1.25" adapter in your 2" focuser. Undo the two screws and lift out the adapter just to see how it all fits together. (It took me several days before I was brave enough to touch anything but the regular EP screw
)
Finally, there is a larger screw (black and plastic on my scope) closest to the body of the scope (OTA). You can use this to adjust how snug or sloppy the focuser is. If it feels too stiff, loosen it; if it feels wobbly, tighten it. You can safely play with it all you like.