This is the FeatherWing Doubler – a prototyping add-on and more for all Feather boards. This is similar to our FeatherWing Proto except there are two! The magic of the Doubler comes when stacking a Feather and another board on top of the Doubler so you can work with both boards simultaneously side-by-side! In addition to the board the Doubler comes with:
1 Doubler PCB
1 set Feather Stacking Headers
1 set Feather Female Headers
The Doubler, like the Proto, has a duplicate breakout for each pin on a Feather, as well as a bunch of plain grid proto holes. Also, the two sets of pins are cross connected and for GND and 3.3V, we give you a full strip of connected pads.
You’ll need to solder on the female headers or stacking headers however you like, the Doubler comes as a mini kit!
This product and description is from Adafruit.