The tool employed to measure the shaft run out is the

The tool employed to measure the shaft runout is the Dual gauge.

Option A: Feeler gauge
A feeler gauge is used to measure the gap width or clearance between two objects. It's not specifically used to measure shaft runout.

Option B: Dual gauge
A dual gauge, also known as a dial gauge or dial indicator, is commonly used to measure the runout or concentricity of a shaft. It provides accurate readings of any lateral movement or deviation from the true center of rotation.

Option C: Micrometer
A micrometer is a precision instrument used for measuring very small distances, typically with high accuracy. It's not the primary tool for measuring shaft runout.

Option D: Caliper
A caliper is a measuring tool used to measure the distance between two opposing sides of an object. It's not typically used for measuring shaft runout.

So, the correct tool for measuring shaft runout is Option B: Dual gauge.