What is it?

This is a 2x7 2.54mm (.1") DIP stacking header. It's intended to be used with boards that use 26 pin stacking headers to lift the extra 14 pins of the Raspberry Pi B+ model GPIO header up to the same level as the other 26.

You can buy this and a 26 pin stacking header together to make a 40 pin stacking header. When butted together the spacing between the adjacent connectors' pins is still 2.54mm.

NOTE: Due to the free domestic shipping, U.S. orders with stacking headers alone require a minimum of 5 (you can mix the two to achieve this). If you order any other product in the same order, this limit does not apply.