The LC-631 is a medium/large nixie tube made by Unitra-Dolam of Poland. It is pin-compatible with other medium/large tubes such as the ZM1042 and the Z5660M.
| Digit size | 31mm |
| Min current | 3mA |
| Max current | 6mA |
| Base | B13B |
The tube comes in at least two variations. One has a prominent getter at the top and so is also slightly taller. You can see side-by-side comparisons in the first four photographs below.