[Solved] How to find a variable using the value of another variable?

What you are wanting to do is not valid C#, rather than have a bunch of properties on "GameData" for "_screw1", "_screw2" you would have an array of screws, each will then be given an index that you could iterate over.

You should also use PascalCase for naming classes. e.g. gameData should be GameData

 private void OnTriggerEnter(Collider other)
     {
         var screws = ScriptManager.GetComponent<GameData>().screws;
         for (int i = 0; i < screws.Length; i++)
         {
             screws[i] = false; // Do something here with each screw
         }
     }

GameData would have something like this:

 public bool[] screws;
 // or
 public Screw[] screws;