What is the name of the mount used for the gyro in an attitude instrument, facilitating free motion in two planes?

The term that describes the mount used for the gyro in an attitude instrument, permitting free motion in two planes, is known as a double gimbal. This design allows the gyro to maintain its orientation regardless of the aircraft’s pitch and roll movements. The double gimbal setup prevents the gyro from being affected by the aircraft's movements, enabling it to provide accurate and stable indications of the aircraft's attitude relative to the horizon.

In practical terms, the double gimbal mount consists of two rings—one that allows rotation about the vertical axis and the other that allows rotation about the horizontal axis. This configuration is essential for the gyro to function effectively in an aircraft environment, where it can encounter various attitudes during flight. Thus, the double gimbal design is fundamental for ensuring the reliability of attitude information presented to pilots during instrument flying.