The most common retractor pretensioner is the ball-in-tube version as seen in the image below. A electrical pulse from the Crash electronics (ECU) ignites a pyrotechnical squib. The burning generant generates a great deal of outward pressure. The pressure pushes the ball in the tube forward over a cogwheel. The cogwheel is connected to the spindle in the retractor and when turning it will extract webbing, up to 120mm.
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