The design of these sections is very straightforward. They are designed to fit end-to-end with other sections, easily forming a long structure that can be used for the crane boom, jib, etc.

The side trusses use a 3-4-5 right triangle geometry. The diagonals are 1x12 Technic beams.

The top and bottom diagonals (members made from plates and liftarms) do not follow a perfect geometry. If you construct this section, you'll notice the top and bottom diagonals do not fit perfectly. You have to force the parts into place, which makes a nice, tight boom section.

These diagonals fall within 5% of having perfect geometry, but can still be built and will function properly. The beauty of these members is that given their composite structure (two liftarms on a 1xn plate), they are somewhat flexible and can accomodate the "unperfect" geometry.

Information on the programs used to generate the CAD images can be found at Ldraw.org.