Step 1. Add the Z top mount (No.A6) to the top of A1. Slowly rotate the rods into the holes, or add some lubricants on the rods. Do not force it, or u will break the acrylic piece.
Step 2. Screw it up with M3 x 16mm screw.
Step 3. Screw up the lock screwon both top and bottom of the smooth rods.