The GS10D is described as a bi-directional 10-way selector tube. The generic name for all of these cold cathode counter/indicator tubes is Dekatron. The GS10D has an argon filling giving a purple glow. The minimum anode to cathode voltage is 440 Volts but the current consumption is around 800 μA.
The construction above the pinch consists of a stack of ceramic discs, each one holding a different set of pins that appear above the top disc in a ring.
The special base with 12 pins, a locating spigot and a central contact for the common anode.
Viewing of the position of the glow is through the top window. However, in this example the window has been coated by the firing of the getter and is not that clear.
A slow camera shutter speed reveals all electrodes illuminated. image courtesy of www.tube-tester.com
The wide glass tube envelope is 32 mm in diameter, and excluding the base pins is 69 mm tall.
References: Datasheet. Type GS10D was first introduced in 1959.