That is a holder for Big Dipper clone of Duet 3 mini 5+ for Flashforge Creator Pro 2017
It fits the printer, but might be a bit tight to fit
Be sure that it is tightly fixed or you can have shorts and the printer will restart over and over again
To fix the board itself on this holder you will need spacers

I used the FlashForge_Duet_adapter as a reference, though I designed the model myself