[Gdeaver]

Over the years have built several arms. We have always used fiberglass pultrusions for the arm material. Never had a failure. One advantage to the pultrusions is that as the load builds they flex along the entire length as compared to AL where they tend to concentrate the stress at the joint. Our driver in 2011 did, while illegal, manage to fork lift a bot. In arms like air plane wings sometimes a little flex can be a good thing especially for absorbing shock loads.