[scook]

An oval head is just like a flat head (like the screws that hold the door hinges to the door and jamb in your house), except that the head is slightly rounded - it humps up a little, rather than sitting flush with the surface it's screwed into. They're asking for the oval head because it gives a nicer finished look - a flat head will work fine, but like MJ says you want one with some non-threaded shank to keep from wearing out the hole in the plastic gizmo. Use a screw or MJ's machine screw with a nut and a little thread lock (or a second locking nut) so it stays put, but use a good stainless one.