The GC10d is a Dektron 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.
The ceramic insulators with connections made to discs between the spacers.
The three sets of guides and the resultant 40 pins around the top of the tube.
The end window with central common cathode.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 86 mm tall.