Drill two 5/32-in. holes through the uprights at each crosspiece position.
Start by cutting the 2x2s to length according to the illustration. Then mark the position of the rungs on the uprights. Drill two 5/32-in. holes through the uprights at each crosspiece position. Drill from the outside to the inside and angle the holes inward slightly to prevent the screws from breaking out the side of the rungs.