Because I now have several - I had to take one apart to see:
"hows it made?"
Three parts; Ceramic Base, Slotted Rotor, and a Cage
The main part is a ceramic block with two metallised plates on the top surface, one on each end. The top slotted ceramic disk is half metallised, and rotates within the metal cage. The cage straddles the ceramic block, with tabs folded over the sides, and one end. The part would normally be soldered on three sides to one connection, and the forth edge becomes the second connection. It takes a very-very small screwdriver to tweak this thing.
This Cap is 2-20pF, 25Volts, and NPO
Which is great for Oscillators!I do not understand the physics of this thing, How or at what point would the disk be at maximum capacitance? A higher power magnifier is needed for a closer look to discover it's secrets.