The GC10d is a Dekatron counting tube where the application of input pulses causes the neon discharge to move around the pin circle. The position of the glow is the readout. At the end of a revolution the tube generates an output pulse to drive another tube. The GC10d can accept pulses up to 20,000 per second and would be used in the first decade of a multi-decade counter.
Each set of guides are joined together and the connection rings are separated by ceramic rings. The anode lead is shielded with ceramic right down to the pinch.
Looking along the pinch.
The viewing window with central anode.
The standard IO base cap.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 83 mm tall.