This is a 20 Position 360 Degree Rotary Encoder, with a nice ‘clicking’ feel. It comes soldered on a PCB, and has a pretty handy select switch (by pushing in on the knob).
The encoder is different from a potentiometer in that an encoder has full rotation without limits. The unit outputs gray code so that you can tell how much and in which direction the encoder has been turned. Can be used to measure the speed and direction of rotation.
Size: 30 x 19 x 30mm