Screw the lower side rails onto the headboard and footboard using the provided screws and wrench. On the inside of the lower side rails, you will see a ledge or series of supports, depending on the brand of your crib. Lay the thin Masonite board on top of this support.
Rest the spring frame on the lower side rails. Slide screws through the pre-drilled holes in the rails and the brackets on the spring frame. Tighten nuts onto the screws to secure the spring frame in place.
Put one side of the crib into place, and secure with screws and the provided wrench. Most 3-in-1 cribs have three pre-drilled holes on each side of the headboard and footboard to secure the sides in place. Repeat with the other side.
Press the included masking caps into place over any visible screws. Place the mattress in the crib, and the crib is ready to use.