Bornyo, those are variable capacitors. Old school ones used in radio tuners at one time. They would be part of an LRC tuned circuit -- Inductor Coil (L), Resistor (R) and Capacitor (C). Since the inductor and resistor would have a fixed value, they used a variable capacitor to change the resonant frequency of the circuit (the frequency of the station desired).

Nowadays, one would use a Phased Locked Loop chip and dispense with all the bulkiness of that part.