A seat assembly for wheelchair of the type having a structure expandable from a contracted condition to an expanded position comprises a pair of tubular members connected to the structure. Each tubular member has a main tubular body, a secondary tubular body parallel to and inside the main tubular body, and an elongated slit extending along both the main tubular body and the secondary tubular body and common to both the main tubular body and the secondary tubular body. The slits open into an inner channel of the secondary tubular body. The main tubular body and the secondary tubular body form a hollow integral piece of composite material. A panel, e.g., of non-rigid material has rods on its opposite edges, the rods having a diameter smaller than that of the secondary tube and larger than a width of the slit to be held captive in the secondary tube, whereby the panel extends through the slit.
