Ever seen a vacuum tube this big?

[N2IXK]

That is a high voltage rectifier diode. Essentially an overgrown 1B3 or 3A3. GE referred to them as "kenotrons".

These guys had 2 major applications, X-ray machines and industrial precipitators, used for cleaning dust and particulates from cleanrooms and smokestacks.

Not particularly high current, as it is a vacuum device not mercury vapor filled like an 857B. This looks like one of the bigger (longer) envelope units, so probably good for ~100kV+ service. Often these tubes were immersed in a tank of insulating oil to prevent breakdown/arcing. They usually have a pure tungsten filament, which glows VERY bright, unlike the thoriated tungsten used for most transmitting tubes. Yours looks to have very low usage, as the glass usually turned a dark brown from all the X-rays they gave off.

If you have a type number, I might have a datasheet for it somewhere in my files.