dr pepper.................... It is NOT a Lamp or Rectifier.
Tony Stewart.................... Unfortunately He Does Not give a Description.
It Does NOT act as a Diode.
Obviously the Top is for a High Voltage Connector.
And You Hold the Knob on the Bottom, So it Must need to Connect to Ground.
This Part is OVER 50 Years OLD.
I Bought it at a Surplus Store, Back in the 1960's
The Middle part of this just below the writing has Two Flat Tipped POINTS inside a Sealed Container with a fixed Diaphragm on the upper side and a Flexible Diaphragm on the lower side.
The Knob at the Bottom Pulls on this Lower Diaphragm to Pull the Lower POINT up or down, to create a Gap Between these Two Flat Tipped Points.
The Inside of this Sealed Portion Has Either a VACUUM or an INERT GAS.
This Gap can be PRECISLY Adjusted Between Zero and Maybe up to 3 or 4 mm Maximum with 10 Turns of the Knob.