Abstract: A frame structure includes tubular elements joined by an efficient tubular joint with internal low mass stiffening members including a central hollow box section. In the more mass efficient embodiments, the box section includes sides forming continuous extensions through the joint of all the sides of the tubular elements and all edges of each side are fixed to the connecting sides at the joint. In less efficient embodiments provided to simplify manufacturing, some of the interior edges may not be fixed to adjacent sides and/or one or more sides may be omitted from the hollow box section. All versions include extensions of at least part of the sides of each tubular element through the joint to provide mass efficient internal strengthening of the joint for use in tubular frames made with hydroformed or other tubular components.