It has strong magnets inside, the electrode sits between them
Answer: It is a Cold Cathode Vacuum Gauge. We use them in Vacuum Braze Furnaces to measure the vacuum in the furnace when it is below 1 micron and moves into the Torr Scale at 3.0 x10-3 and lower.
after drilling a hole inside the screw. A reamer has sharp ridges and are set in a clockwise direction