What are they for? Stacking. You put the headers on top of your Arduino and then you can add shields like our Protoshield or our Motor Shield or our Proto-Screwshield (pictured above) to get your Arduino doing all the cool things you want it to. Our set includes 1x 10-pin header, 2x 8-pin headers, 2x 6-pin headers, and one 2x3 header.
The legs are all 10.5mm long, so after PCB thickness (1.7mm) you have a height of 8.8mm - just enough to clear the Arduino's USB-B connector. They€™re also fully compatible with shields designed for Arduino R3 and the Leonardo. For shields that don€™t use the 10-pin header or 2x3 header, use the 6 or 8 pin ones.
Some experimentation might be necessary to get these working. For example:
Really, the possibilities are endless, just keep in mind that you may need to do some adjusting of code to handle the multiple devices and that there may be pin compatibilities.
Identical to SparkFun part PRT-11417.