ISO 9999 codes:
12 Assistive products for activities and participation relating to personal mobility and transportation,
12 24 Wheelchair accessories
Source:
How to Make It Cheap Volume 1 - - - Full text at https://archive.org/details/cheap-manual-vol-1
How to Make It Cheap Volume 1 - - - Full text at https://archive.org/details/cheap-manual-vol-1