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The design employs Lewis Hamilton and Button to close off a vent in the cockpit of their car using their legs, which in turn helps to stall the rear wing for extra straight-line speed.
As it is the drivers doing the moving, rather than any part of the car which would be illegal, FIA race steward Charlie Whiting has given the McLaren the all-clear.
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thx... The issue that is causing concern is not just about the slot in the rear wing of the car.
In fact air is believed to be taken into the car through a vent in front of the cockpit, it then goes through the car and out of the back of the engine cover.
The system - which speculation says can also be influenced by the drivers - affects the airflow to the rear wing, giving the car less drag, and therefore a higher maximum speed, on the straights.
All 12 teams on the grid have had all their cars passed by scrutineering ahead of Friday's first practice for the Bahrain Grand Prix.
A McLaren spokesman said on Friday that the rear wing design had "never been an issue" although Red Bull team principal Christian Horner claimed earlier it had caused "a bit of a fuss".