This is a chemical ionization electron impact ionizer for a quadrupole mass spectrometer I helped design and later assembled and tested as a 20 year old.
Running that outfit's precision assembly department was my first venture into management and I was the youngest employee to ever hold a management position with them.
I worked hand in hand with the engineering department on a daily basis because they needed real-time input of any part of our process.
All of the threaded fasteners and potential air traps were drilled for venting in a ten to the minus 7 power torr vacuum chamber.
It used nickel, platinum, tungsten, vespel, ruby sapphire balls, machinable glass and 304 series stainless steel for the construction.
We used an 18 step cleaning process to prevent any outgassing which would contaminate the test samples and they were assembled and chambered in a class 10 clean room.
We always rough tuned the mass specs to the water peak then introduced at least two test sample gasses to complete the calibration.
It took about 40 man hours to build one, involving spot welding and a lot of hand work fitting the electrical connections, screens and grids.
The 304 stainless was nasty to work with because of how readily it would gall threads when it was clean.
Our large fasteners were 2-56 (2.2 mm dia)and we used a lot of 0-80 (1.5 mm dia) so they were actually tiny to boot.
The 20 pins on the bottom allowed it to be quickly detached from the quadrupole filter for cleaning.
This one was superseded by an improved design about six months after we started using them because the gas porting for chromatography proved to be a failure, so it was considered scrap and made it into my collection.