This is the casing for the 5V RAIL D1M BLOCK. It allows the 5V pin to be connected to an external power source. The range of voltage that the Wemos D1 Mini (5V pin) can operate on (and the regulator handle) is ~3.0V to 5.5V.
I primarily designed this for battery operation where the battery is charged via solar cells and a TP4051. I can see this being useful where more current is needed on the 5V rail directly (like adding 4 off MQ-* sensors via an analog multiplexer at 100mA each).
These [components](http://www.iot123.com.au/MT_D1M_5VRAIL), a PIN JIG for soldering, and 2 off 8 pin 10mm Long Needle Female Pin Header Strip are required for this build.