Dela has it just about right - the only clarification is that the center anchor screw threads through the base plate into a small insert under the plate. The anchor screw is fully threaded with a socket cap, but from the top looks almost like the pivot points height screws without heads.
Jfoster - you can order a nut blank from us that you can install on any bass, but mind you, it's not an entirely easy job and should be done by a good guitar repairperson. For a 4-string the nut blank is $45, and for reference we charge $75 to install one.