Tetra quick release is an adapter that is attached by the hub of the rear wheel and holds in the release button when removing the wheel.
See also www.panthera.se/en/tillbehor_tetraQR_standard.html (last checked March 2017).
Used for purposes such as riding in a car, when the user lifts the wheelchair into the car, see www.spinalistips.se/tips-lifting-the-wheelchair-into-the-car-en-598.html
Panthera, Etac, www.panthera.se/index_en.html (last checked March 2017)
This tip is from 2012