The IN12 is the Soviet analog to Western oval Nixie tubes such as the Burroughs B5991 and 8422. To save on costs, the tube does not have a cathode to represent the number '5', instead an additional '2' stencil is used, mounted upside down. Digit height is 19mm and the diameter of the tube is 30mm at it's widest point. This tube is actually mechanically compatible with the 14 pin sockets used by the B5991, though the underside nipple requires that said sockets have a centrally located perforation for clearance.