The BEI Sensors/Sensata part 01039-1951 is an Incremental Rotary Encoder with a 2.0 diameter. This encoder is from the Express-H20 series, which is known for its high performance and reliability. It offers precise and accurate position feedback for various industrial applications. With its compact size and robust design, it is suitable for use in stringent operating conditions. The incremental output signal allows for easy integration with a variety of control systems. Overall, this encoder is a durable and efficient solution for accurate position sensing and control.