The Nixie tube is a cold cathode numerical indicator tube. The term Nixie tube became generic for this class of display.
The construction is of a common electrode normally the anode, and a series of shaped cathodes. Each cathode being in the shape of a number from 0 to 9. This were stacked on support rods and each cathode was brought out to its own pin. Energised by around 180 volts a open collector based TTL chip would interfact between the digital circuitry and the display. As each cathode was connected to ground the glow of the neon gas filling would form found the cathode and through the end window the shape of the numeral would be visible. They were very successful.
Seen end on the mesh is clear as are the ceramic insulators in the lower part of the envelope. The cathode planes fix to these insulated supports.
This shows the base and the arrangement of the 14 pins.
The end window envelope is 20 mm wide and 26 mm long. Front to back excluding the base pins it is 22 mm tall.