This unit attaches to the gas height adjustable stools for adults and children. Application: Retro fits both 20642 plus 20645 stools and provides lumbar support for the spine. This has been designed in co-operation with educators to aid spinal support and good playing posture. Specs: Extra heavy duty L-bracket with curved cushioned top. Attached with 2 Allen-style bolts with positioning options and supplied with adjustment key. Dimensions of cushion: 28 x 7 x 7cm Height of cushion top off seat: 17.5cm