The Sidi Crank Brothers Cleat Spacer is pretty simple, and pretty self-explanatory. It's manufactured by Sidi specifically for those customers that wear Sidi shoes and ride Crank Brothers pedals. Because the Crank Brothers Cleat sits so close to the sole of the shoe, Sidi noticed that some customers would actually wear a groove in the sole of their shoe. So, Sidi developed this cool little wafer crafted from brass that fits snugly between the cleat and the sole of the shoe. While it is not mandatory, it is strongly suggested, especially for those of you purchasing the full carbon soled Sidi Dragon II SRS Carbon. 4g for the pair.