Use the headers on the Feather M4 to help install the socket headers to the Doubler FeatherWing.
Carefully fit the socket headers onto the male headers.
Install Doubler FeatherWing
Place the Doubler FeatherWing over the pins of the socket headers. They should be fitted through the pins.
Secure PCB for Soldering
Use a PCB vise to secure the Feather with the socket headers installed.
The Feather is secured face down with the pins from the socket headers facing up.
Place the Doubler FeatherWing over the two rows of pins. The silkscreen should be facing down.
Solder the 12-pin and 16-pin socket headers to the pins on the Doubler FeatherWing.
Soldered Set of Headers
Check the solder joints are solid and each of the pins has been fully soldered.