Insert a M6x12mm Hexagon Socket Head Cap Screw into the inside of the z-motorholder and screw a T-Nut to it loosely from the outside.

Repeat this step for the second z-motorholder.

Place a M6x12mm Hexagon Socket Head Cap Screw in one of the two holes of the corner bracket and screw a T-Nut loosely onto it.

Repeat this step for the second corner bracket.