This sensor is composed of an infrared emitter on one upright and a shielded infrared detector on the other. By emitting a beam of infrared light from one upright to the other, the sensor can detect when an object passes between the uprights, breaking the beam. Used for many applications including optical limit switches, pellet dispensing, general object detection, etc. Gap width = 10mm
With the included breakout board, 3 pin male header and 220 Ohm resistor you can get using this sensor in no time, simply solder the kit and you're good to go.