This is a case for dual channel relays, particular “2 Relay Module”, black board. It is designed to hold the module in place by pressing the top and bottom parts together only.
The case consists of 2 parts that are screwed together with four M3 20mm screws and nuts. All holes can be used although to mount the case on a surface or build plate.
There is an additional bottom plate with two mounting supports on each side and holes spaced 55mm between.