https://www.pololu.com/product/1419This reflectance sensor module is designed for use with the Zumo shield for Arduino. It has six IR LED/phototransistor pairs that can be used for line following or edge detection; each sensor provides an independent, digital I/O-measurable output.
Universal mounting cube made from hard plastic (HDPE) for fixture of various small electronic sensors and modules, specialy for perpendicular positioning. Dimensions are 10x10x10mm and it comes with included screws for mounting (M2 for sensor). It is sold in pairs.