Yaw Indicator, Kollsman 254BK4-056
Here is an aircraft Yaw Indicator, made by Kollsman, used to indicate the direction of yaw of the aircraft in flight. Yaw is the deviation, or 'twist', left or right, of the aircraft's center axis with respect to its forward direction of travel. Measures 3.25in diameter and ~3in deep. It is driven pitostatically....as pitotstatic pressure or vacuum is sensed at the rear ports, the pointer moves left and right.
Was acquired in a bulk purchase during US military air base closures during the 1970-80's, so likely from a US Navy or US Air Force aircraft. If you know what aircraft used this indicator, let us know!