[Mister Moose]

If I remember correctly, the inner star ring holds the glass. If that isn't tight enough, you won't be able to fully tighten the gauge with the outer ring, the star ring will move. And as others have said, the threads must be clean and lubricated so that effective sealing (while level) occurs before max toque is reached. And the tightness of the star ring will be one factor that determines max torque.