There are other relay case, but since i use it to power on and off equipment with an 220V extension cord I wanted to protect the 5V relay board and let some room for the power cord.
To customize, measure the board size and the distance between the holes (defined in the support part). I have different clone of this board and the hole spacing is not exactly the same (20 or 21 mm).
The support pegs are centered according to the global width.
No support should be needed if the hole for the pin is not too wide.