Abstract: A duplexer includes a cavity resonator defining an opening covered by an RF plate. The RF plate defines an opening through which a pass-band tuning pipe extends and is secured thereto. A collar is attached to one end of the pipe, and at least one steel set screw extends into the interior of the collar, the at least one end having a soft (e.g., brass) tip. A tuning plunger is slidingly positioned within the pass-band tuning pipe. A rod is attached to a first end of the tuning plunger and extends through the collar, the rod being fabricated from a material harder than the tip of the at least one set screw. The at least one set screw is configured for tightening down on the rod to secure the rod and tuning plunger in place. A trimmer capacitor is positioned in the RF plate.