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What is the ISOFIX system?

The main aim of the ISOFIX system is to avoid errors in installing child restraint systems, which often occurs when they are installed with seat belts and the manufacturers' instructions are not followed. These are the characteristics of this system:

  • There are two anchors or rings attached to the vehicle. These anchors engage with the child car seat by means of rigid bars which are pushed against the rings and locked with a simple click.


  • In addition there is a top anchor (Top Tether) or a bottom anchor (Support Leg) to avoid the seat turning or tipping over.

Top Tether:


Support Leg:


The ISOFIX system is usually used with the smallest child seats, namely those that form part of Groups 0, 0+ and I. For larger seats, we usually see a combination of this system and the seat belt.


Child seats in groups 0+ and I with the ISOFIX system are divided into Universal and Semi-universal, depending on where the third anchorage point is located. It it is located at the top, the Top Tether, it is a Universal seat, and if the anchorage point extends from the vehicle floor to the base of the seat, it is considered a Semi-universal seat. A Universal seat means that the seat can be used in any car that has the third top anchorage point while a semi-universal seat can be used in a number of vehicles, but not all of them. In this last case, the child restraint system manual includes a list of vehicles in which the seat car seat can be used with the ISOFIX system.

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