Front panel vs rear panel connector
This is a case of "does it mount to the panel from the inside (Rear) or outside (Front)?", not "is the panel on the front or rear of the box"!

The rear panel-mount part installs from inside the box and has the jam nut on the outside of the case; the front panel one installs from the outside of the box and has the jam nut on the inside... It is that simple.