I created an extrusion, going on extrusion and setting two reference planes. I assigned the dimensions, which parameterize: Length : 4000 cm Width : 200 cm I gave 250 cm of thickness to this object.
I created the buttonholes for the screws.
Then, I did, extrusion > circle. From properties > solid > void I could create an object that can pierce the previous one.
With the cut command, I select the two objects and create a void.
Now I create the "mother" part that will support the "child" object, starting from metric generic model.
I created the shape of my object mixing diverse elements. The child object will be stick to this part after it.