Seat Belt Retractor: Description and Operation

Typical Retractor:

Lap/Shoulder Safety Belt Retractor Assembly, Front - Active Restraints
The safety belt retractor is designed to let the webbing move in or out freely, except during sudden vehicle deceleration, when it is automatically locked by a mechanically actuated inertia sensor.

The 3-point system (lap and shoulder belts) is used for front and rear outboard seat positions.

The three anchorage points are: the retractor, floor anchorage point, and the lap belt buckle.