It's near the socket for the CRT of an old BW computer monitor. On the PCB, the capacitor are marked Cxxx and these are marked SGxxx. Anybody knows what they are and how they work?
They are used to prevent arcs between the elements of the electron gun in a CRT. Arcing could damage the CRT by causing the beam to turn on very hard and burn the phosphor. The arcing could also damage the video amplifier.