The lower tethers are needed to properly install the seat if there are no attachment loops in the vehicle. They are attached to the floor of your car so that you can attach the retracting lower tethers of the seat to these anchorage straps.

One pair of lower tethers are included with the seat. If you have several cars, it might be convenient with an extra pair of lower tethers so you don’t have to de-install them each time when moving the seat between vehicles. Buy an extra pair if needed.