A microwave resonant cavity includes a conductive shell with a screw hole having first threads and a screw having second threads configured to engage with the screw hole. The conductive shell defines a volume, the screw extends into the volume, the microwave resonant cavity has a resonant frequency, and the movement of the screw changes the resonant frequency. The first threads have a first pitch, and at least a portion of the second threads has a second pitch different from the first pitch.