Plastic.
In a few cases, the tool needs to go into a coil and adjust a ferret bead inside, manipulating the magnetic field around the coil. Using a metal tool will interfere with the magnetic field you are adjusting and it will never get properly adjusted.
The other reason, some of these adjustments needed have high voltages. Using a metal tool is just asking for trouble. You have not lived until you improperly discharge a CRT and get a 4KV Shock into your hand from it. The pain will be something you will never forget for the rest of your life and you will give that part a lot more respect than needed.
Finally, a metal tool can break these adjustment points. thing turn from one stop to another (except for coils, you can turn it until the bead comes out and then you need to put it back in!). If you turn it until it stops and it still needs more adjustment, its another component to find and replace, but mentally you will want to turn it until it breaks, and you will. With plastic tool, then you get to that point where it stops, and you try to turn it some more, the tool will bend, telling you to end it there.
In a few cases, the tool needs to go into a coil and adjust a ferret bead inside, manipulating the magnetic field around the coil. Using a metal tool will interfere with the magnetic field you are adjusting and it will never get properly adjusted.
The other reason, some of these adjustments needed have high voltages. Using a metal tool is just asking for trouble. You have not lived until you improperly discharge a CRT and get a 4KV Shock into your hand from it. The pain will be something you will never forget for the rest of your life and you will give that part a lot more respect than needed.
Finally, a metal tool can break these adjustment points. thing turn from one stop to another (except for coils, you can turn it until the bead comes out and then you need to put it back in!). If you turn it until it stops and it still needs more adjustment, its another component to find and replace, but mentally you will want to turn it until it breaks, and you will. With plastic tool, then you get to that point where it stops, and you try to turn it some more, the tool will bend, telling you to end it there.