In 1993 the seat frames were changed and although the base frame looks very similar to earleir models, there is a difference in the shape. At this time the seat diaphragm was changed to a special rubber/woven design known as the "Suisiara" model. The idea is that the woven red area stays rigid while the black rubber area expands with weight on it. The unit comes with the necessary metal clips to attach to the frame. The original diaphragms are no longer available and has been replaced by this newer looking design (rubber no longer down the middle).