"Dynamic Hardware is available on Solid Backs with Knob Release Hardware and frame widths between 12 and 18 inches. Three different spring tensions are available to accommodate users from 40 to 250 pounds. This hardware provides shock absorption caused by excessive tone spasticity or by repositioning. It extends the life of the wheelchair and Basic Insert by reducing stress on the wheelchair backposts. Not available with backs that are curved by wood. (Curved by foam and most other modifications are available)"