The GI-21 is a numeric nixie tube manufactured by National Union. It is one of the first nixie tubes ever made. The digits are hand made, and the size of the tube is relatively large. It can display 0-9. Driving the GI-21 is not very easy, because it has no anode-grid and the other digits have to be used as anodes. Along with the GI-21, National Union produced the GI-10 and maybe the GI-11B, both are smaller. This tube is very rae