This is a simple holder plate for the lm2596 module it fits the MH one like this one (http://www.aliexpress.com/item/LM2596-DC-LED-Voltmeter-4-0-40-to-1-3-37V-DC-DC-Step-Down-Buck/32593909002.html?)
It´s to make it more stable and to secure it from short circuiting from anything laying under it. To secure the module in place I used really small screws from an old salvage projects. If you don´t have any you could just glue it in place.