Hi David,
Maybe you missed Akild's expalannation of the capacitnde issue.? The electrodes are fixed to the side plates. The spacing is changed by adding spacer rings. Thicker spacer? bigger gap and les capacitance. The document Jim provided a link to?
Has a mechanical drawing on page 27 which shows the connection details. You can calculate dimension S (electrode diameter) from the stated air capacitance with different spacers.
